How bad is algae at 2 WPG?

That's a loaded question, becaue the answer really is 'it depends'. IMO, it's definitely doable, but you have to be patient and know what you're doing

What does it depend on? Pretty much any factor you want to think of from water chemistry to substrate, photoperiods, how you set up the tank, age of tank, etc...

If it was me, I'd start with just adding the 2x32W for now, totalling ~ 100W. The more light you have, the more quickly things can go south if there's imbalances or problems. You can get away with the 2wpg, but you will have to add excel at least. Wtihout the extra carbon, the plants won't be able to grow well enough to keep up with that light, and algae ensues. Nutrients will also be an issue, although it sounds like the nitrate portion is OK, PO4 & Fe will need to be addressed. That's where substrate, tap water, feeding amounts, etc comes into play. If you're not planning on adding lots of plants, I'd go easy on the light.