Is it okay to run a 12-2 wire directly to each outlet from a panel box or do the outlets in a circuit have to be wired in sequence?
How many hot wires can be terminated at the breaker in the sub-panel in the garage?
Since I'm not an electrician (I will have a friend who is one double-check the work prior to requesting the rough-in), I ran all the wiring from the panel box location to each receptacle/outlet individually (then realized what I had done.... :( )
The circuit breaker itself will have specification for how many wires it can support under the lug, typically just one, and what torque you need to achieve.
I'm really confused as to why you would home-run each outlet unless you plan on having a dedicated breaker per outlet. If it's all going on a single breaker then that's a huge waste of wire. Receptacle boxes are approved junction boxes.
As for the old 12-2, ask the home inspector since you have to appease them, not randoms on the Internet. I would verify that the sheathing is in good condition and verify the gauge using your wire stripper holes.
FWIW, the home inspector could easily say:
I am unable to inspect the sheathing, re-do it with new wire.
In home wiring, the route of cabling is in a "tree topology" meaning there are unlimited branches, but no "loops back to itself". Reasons below.
A vine topology (one long string) is one kind of tree, but it's not required.
So yes, you can branch as many cables as you want anywhere you want, as long as the junction box has the required volume (2.25 cubic inches per wire for #12) for all the wires.
Yes indeed, you can branch like that at the panel. However, the breaker itself is limited to 1 or 2 wires on its terminal, so you will need to pigtail to add more than that.
A word about spaces on the neutral bar. This is a really good way to run out of them, and this might lead one to... errors. Grounds can be moved to accessory ground bars (and will be if it's a 4-wire-fed subpanel). Other than that, your options are limited. You cannot double-tap 2 neutrals onto a neutral lug. You cannot put neutrals on accessory ground bars. You may be forced to pigtail neutrals to the lug. However all neutrals on a pigtail must be from the same circuit and you need to have good discipline on that.
Now why is it this way?
Because wires throw magnetic fields proportional to current. DC wires throw DC magnetic fields (think: refrigerator magnet). AC wires throw constantly pulsing magnetic fields, causing a maelstrom of magnetism that causes heating of metal things nearby, vibration of wires (leading to cracking, overheat, arcing), etc.
However...if current goes out one wire and comes back another wire in the same cable, those magnetic fields effectively cancel each other out. So the system is required to be wired like that, giving a cabling topology like a tree. Unlimited branches but current must come back the same branch it came down.
There are a few different issues here:
Old cable - that has already been discussed, and will be a decision for the inspector, unless you redo it with new cable before inspection.
Separate home runs vs. serial
This is where it gets interesting. Arguably a series of receptacles saves wire. I can easily see a split - 2 runs per breaker. For example, use 2 20A breakers, with each having both a "left side" and a "right side" run. That way you have receptacles on each breaker on each side of the garage, so that if you are working on one side or the other you can run two high power devices at the same time without tripping a breaker. Beyond that, multiple runs are generally a waste of wire since they don't increase the capacity of the circuit or make the circuit any more useful. There might be an exception with a bunch of small rooms, but in a garage running cables through the walls from one receptacle to the next is generally very easy.
That being said, you have to understand that serial here is not the strict (computer) definition. Really it is a tree configuration. Even if you run one cable to one side of a receptacle and another cable to the other side, they are functionally at the same level. With the exception of a GFCI/receptacle, the receptacle plays no role in getting power from one cable to the next except as a simple conductor. (Even with GFCI, as long as there is no ground fault, load and line are effectively the same.) This is important because occasionally we see situations where a receptacle is wired in such a way that it truly is a series load - i.e., wired incorrectly, against code, and a major problem. If that is done then (a) the second receptacle may not work at all if there is no load in the first receptacle and (b) there are some major problems that result from doing this.
So as long as you understand what "serial" means in this context, that is the preferred method.
There is actually a big advantage to multiple home runs if every home run gets its own breaker. That actually can make a lot of sense if (a) you have a really big and (b) you can use ordinary breakers. A big panel is easy. You can have a 30 or 42 space panel as a subpanel, just like you can (if it can be converted to use a main breaker) use a small panel as a main panel. The cost difference between small and large panels isn't usually very much in the overall project cost. However, the breaker type matters a lot. A panel might use $5 - $10 ordinary single pole breakers but $50 or more AFCI breakers. Generally speaking, circuits in a garage will require GFCI, but you can do that at a receptacle for a much lower cost than at the breaker. However, in some jurisdictions (depending on NEC version and local rules) you will AFCI protection, which is almost always done at the breaker. In other words, if you only need GFCI, the extra cost for a split (2 circuits with one receptacle each instead of 1 circuits with 2 receptacles) might be $25 but if you need AFCI as well then it could easily be twice as much.
If you decide to use multiple runs with a single breaker, you just need to connect the wires before they get to the breaker. That can be done in a separate junction box, but as I understand it there should be no problem doing that in the subpanel box.
If just to have outlets in the garage then they should be together, wire goes to one outlet then to the next.
If needing outlets to power high amp(16 amp) machines then one outlet per breaker can be done.
Garage outlets need one GFCI protection(breaker or outlet) per circuit.
No, cables to outlets are not required to be run in a sequence. Nor is there any inherent benefit to doing so. Since A/C wiring is always in parallel, it doesn't matter at all how the cable gets to a particular outlet. In fact, you'd be hard-pressed to find a case that doesn't have a branch in the topology.
Therefore it's merely a matter of relative position, and not wiring sequence, since the logical circuit diagram is the same regardless, with each outlet's terminals having a direct path to the breaker (not passing through any other load). You should pull cable to the outlets however results in the best use of the materials.
Most outlets only allow one hot wire connection, though. If you end up with multiple cables at the panel, there are several ways to deal with that.
You cannot connect more wires to a breaker than is specified for that breaker, which is usually one. If you've already done the wiring which appears to be the case, there's no reason to redo it. You can bundle the hots and neutrals to single wires with wire nuts and connect the single wires to your breaker and neutral. Might be nice to leave a note as to what's going on here. Leave slack in the panel so you can reach any breaker position in case you want to convert to dedicated circuits. Since you'll need GFCI protection, you can connect to a single GFCI breaker. Since you've run 12/2, you can use a 20 amp breaker but can use 15 amp duplex outlets.
