You should keep nori for the Tangs if any survived. The GSP will likely be fine, may hide for a week or more but they are like a weed...(certainly a cool one, I really like them myself)
The 1.0 if accurate is certainly bad news... (.20 can be fatal to some fish and .5 is scary high)
Nitrates are not going to be much of an issue with just the GSP, however if you go with any SPS or other stoney corals, you will need to keep them at 20ppm or under. More live rock will help with that as the algae will hurt the coral as much as the nitrates normally. (over grows the polyps) Depending on the rock (porosity) you have, 1 pound per gallon of tank capacity is suggested minimum and some of this really heavy stuff can be double that. I use old reef bones and is very light stuff with a lot of porosity.
My SPS tank had around 15G worth of frags when I sold it all out about 2 years ago. I had it up and stable for about 5 years without any issues at all.
A good quality skimmer is a MUST have if you are going for any SPS corals and you will need the rock too... It gets exponentially expensive as you get better livestock... Total system cost for that tank (220G) was around 25G's
I did find that the cheaper skimmers (needle wheel) work just fine. No need to blow $400 on one with skimmers like the Corallife 125' or the 250.. they work great for under $200
Patience is the biggest factor... nothing good happens fast in a marine tank
Oh and if you have not already... Invest in a decent RO/DI unit (75G per day, not the 100's)