I can't help you since I just detail on the side but your website is one of the best I've seen from the posters on autogeek and i am sure you will do great if / when you start working full time.
Do you really get a lot of people paying for oil changes?
Yes, you need to fix your website and get a nicer camera to show detailed work of how well of a job you do.
You can get an excellent camera for ~250-300$.
I did not know that about yelp, however I am not a pro detailer I work at a used car dealership, but next door to us is a smog shop that uses Yelp and google, and he is very busy and is the among the busiest smog shops in my area and he says the majority of the people come from yelp.
I use Verethane spar which worked really well so far on the 3 headlighes I have done. You can still buy the Minwax spar varnish but only in the spray can.
I hope you do not take this the wrong way, just giving you my opinion:
IMO - do not spend any money on advertising and spend some $$ on your website. Your website has lots of info but it does not look proffessional it looks a step above someone doing this as a hobby on the weekends. After that...
I went to my local home depot and they say the wipe on (can) version is unavailable.. has anyone had any luck finding it? I grabbed Verathane which seems identical just a different brand. Lowes does not carry this any more either, same goes for walmart.
You need a special oil separator we have one at my location. Learn a bit about engines, it will help you a lot. Don't get electrical things that wet, dry fast with air. Clean top of engine when cold. When trying to clean underneath oil stains let the car idle first to make the oil looser.