Question 1 no. Question 2 "look at the nameplate".
The rest of this answer is a frame challenge - that's why it doesn't 'answer the question'. The frame challenge is: No, you can't do that. Code says you don't get to invent your own self-styled technique for doing load calculations. You have to do it by the book.
Noting that a generator is involved, there's another book too: your power company's Service Agreement / Rules & Regs.
Automatic transfer switch
With an automatic transfer switch, Code absolutely requires the generator be large enough to pick up "the entire load to be served". That's because you may not be there to run around turning off water heater, A/C etc. to stop the engine from bogging.
What is "The entire load to be served"? That is definitively answered by a Load Calculation on the house. The Load Calculation is a standard procedure in NEC article 220 that requires an inventory of large loads, a fixed allocation for kitchen, bathroom, laundry 120V circuits, and then "3 watts per square foot" as a catch-all for lighting loads and miscellaneous receptacle circuits. So you don't need to find the nameplate on your laser printer or cable box; that's in the catch-all.
"Throwing all your loads on and clamping your service wires" is not a substitute for a Load Calculation. There is an allowance in NEC for observed loads, but it needs to be better done than a one-time "clamp job".
There are a couple of exceptions. First, the Load Calculation itself allows loads to be excluded that will never run simultaneously; such as electric heating and (obviously electric) air conditioning.
Second, for "generator sizing" purposes, you can exclude a load wired through a "Load Shed" or "Demand-side management" device. In the simplest form, it's a box you put in front of the dryer or water heater that automatically disconnects them if AC power frequency and voltage suggest a lugging generator.
In the more complex form, you have emerging technology like Eaton, Square D, Leviton and Span's "smart service panels". The boutique product is the choke gulp $6000 Span service panel, where every breaker has energy monitoring and programmable disconnect. You can tell the Span "When on generator, don't let the house exceed 6KW". As obscene as the Span's price is, it solves problems that might be even more costly to solve otherwise.
Manual transfer switch (much easier)
However, if you are using a manual interlock or transfer switch (Square D or an aftermarket maker will make an interlock for that panel in the $60-80 range; that plus a $12 breaker takes care of that requirement), then you are allowed any size generator you want, since you'll be presumed to be there to cut off the water heater if it cycles at an inopportune moment.
Note that from a sizing perspective, if you get a generator that is capable of 9.24 KW (38.5A @ 240V), it will not be able to carry a split load of 30A and 47A. At the risk of stating the obvious, 47 is larger than 38.5.
