A sub panel is great for adding shorter runs. It add 220/240 if you want. I use it on my bass amps.
Romex is for running on it’s own. No conduit. There is flex armor that meet code in the bay area.
# 10 is great for a subpanel feed
# 12 for 20 amp circuits
# 14 for 15 amp circuits
Use copper not clad they sell that crap everywhere. COPPER, not cryo anything just Copper romex or if your going to use conduit use the correct wire for inside conduit or Flex armor. BTW a lot of the new flex armor is aluminum with copper clad..
ALL grounds must be tied at the main
Any breaks in runs must be put in a box
ALL boxes must have a 2 hour fire rating
It’s actually easier for me to run the wire in the wall after it’s all said and done. You just have to ask someone that knows how to string wire without tearing up the whole house. It usually involves a couple of fancy drill bits and just a little patience. Time wise there is an increase but only because of drywall mud setting. I’ve used hot set mud and only had to primer and paint, still a 2 day wait.
PERMITS: Permits mean you bought permits and paid for something. It doesn’t mean you got anything for your money. The home, building or any thing else could burn down and take out half the neighborhood and the inspector is responsible for absolutely nothing other than looking (if they do at all) and signing the little box. My neighbors house was worked on by a contractor, signed off on by the city and caught fire within a year.. THREE issues all via inspection after the fire. All boo boos, caused an electric mickey mouse clock to burn the joint up. You can get a loan easier for selling or buying if you use OPM, I don’t. Pretty simple.
Sell a house or buying one, I pay cash. I buy "AS IS" I sell " AS IS". I have for 50 years and 22 pieces of property. Same goes for most of the people I deal with, unless I carry the paper or something.. We both shake hand call each other suckers and wait until the next time we meet.
Regards