My angle valves under sink are hard to reach with garbage disposal in the way.
Can I turn the water off at the street to change parts in faucet, or will this drain my gas hot water tank?
I shut mine off at the entrance to the house, rather than the street. The hot water tank has some elasticity to it, so it will hold a little "pressure" but that will bleed off with a faucet open. If you wish and are able, you can drain down the system by opening a faucet that is lower in elevation than the one you are going to repair. This is usually not necessary.
A couple of tips. Slowly reapply pressure, not just in case what you fixed is leaking, but also so that the hot water tank doesn't get a rapid change in pressure. Also you might want to put the hot water tank on pilot, rather than ON, while doing your work. You do not need to drain the tank. If it is above the faucet you are going to repair, it may be necessary to turn the water off on the tank. Usually this is not necessary. (Example of when it is: You are fixing a faucet in the basement, and it is located below the top of the hot water tank. In that case, you need to close the valve out of the tank. But you do not have to drain it.)
Slowly open the faucet after you apply water pressure, so that any air is bled out without hard slugs of water causing hydraulic banging in your pipes. If you leave a faucet open, you may end up with splatter on walls and floors from water and air coming out of the faucet when you first turn on the water.
Good luck with your repair.
You can turn the water off at the street / meter. My last in town home I had to do this many times. First I recommend putting the water heater in pilot mode. With the water heater in pilot you won't have to relight the pilot and this will protect the tank if your project takes longer than expected. After the main is turned off open a tub valve or one that is lower than the sink this will depressurize the lines. when you open the sink the water in the line will will drain to the lower tub or hose bib and there will only be a minor amount of water left in the faucet. Having the lower valve open also helps if the main valve will not fully seal the small amount of leakage goes to the lower valve that is open. Repair your faucet but leave the valve open when done. Turn the water back on at the main/ street. By the time you return most of the air will be purged out of the system. Close the tub or hose bib, by the time you get to the sink that air in the sink line will probably be purged. Note opening and closing the main valve may break loose some scale/ rust, you may need to clean the ariator on the sink but tubs don't usually have them, verify no leaks on your faucet and check the main valve, I have had the valve packing leak after opening and closing if leaking you might need to tighten the packing nut. This method with a lower drain open is the least messy method I have found because many homes the main valve is not cycled often and many have small leaks that if a lower tap is not opened water ends up on the counter. If everything looks good turn your water heater back to your desired temp and enjoy the thought you saved a bunch over having a plumber do this repair.