Looks like a good purchase. You have a solid regulator. I would add an octopus to the reg but after talking to your instructor. If you want to stay with the SP line, consider the R095 or a R195 which would be the most economical route. Or you could use the 550 as an octopus and buy another second stage to use as a primary. You can also go with another brand - most will be compatible. Just ask your shop.
At the same time, ask about the air2 as it may need to be serviced. For me personally, I would rather have an octopus/secondary second stage on my reg and a basic inflator system on my BC but YMMV.
If possible, test some standard fins and compare them to the split fins and see which ones you prefer. Buy your mask at your local dive shop. The most important consideration is fit and you cannot do that online. Forget about price and looks and go for the fit. A $50 mask will be as good as a $200 mask.
Tanks appear fine assuming they were not made prior to 1988 or so. You may want to ask the seller if the valves have been serviced - maybe during hydro. If not, just something to watch for. Not a big deal to service them and they can take some abuse.
I know nothing about the computer other than it being a quality brand but check the battery life. You may or may not want to use the pressure gauge in addition to the AI computer - maybe another question for your instructor.
Rinse your wetsuit after use
Also, a lot to be said about supporting your local dive shop as they are the ones who will service your gear, give advice, give something a quick look, etc.
Enjoy and welcome!