You’re smart if you’re asking these questions. Mark up of 30% is reasonable for most stuff but some things are okay to mark up much more than that. Trust your judgement, fluids shouldn’t be where you make your money. Brake pads, rotors and radiators should be more of a money maker if that helps give an idea. Hourly rates can vary a lot depending on where you’re located and what you’re specializing in, if you have people in the business local to you don’t be afraid to call and ask what they charge per hour. Be up front and honest and for the most part, guys in the business will try to help you and the ones who don’t are scared you’ll steal their work or something and probably aren’t all that successful anyway. Congrats for taking a risk and betting on yourself, I’m rooting for you.

I’d pull out all the dash cam stuff first to 100% rule that out. Accessories really is most likely the cause of battery drain.

Change all the coils and plugs if you plan to keep the car….

Piston rings are on their last legs. Drive to a new car and buy it while you still can.

Bleed your cooling system first, if that doesn’t fix it than change your thermostat. Once you fix it sell that car, they’re not very good in my opinion.

This is a screw job. Buy a Haynes manual and get familiar with Rockauto save yourself money.

Keep the receipts for every oil and filter you buy. That will show the record to a potential new buyer. If that’s not good enough for them find a different buyer.

Sounds like head gasket might be leaking. Is the coolant mixing with the engine oil?

Other comments here are all very good but I’m Just offering a different idea/possibility here; does the car show that it’s in gear or in park? If not, maybe you need to replace the neutral safety switch.