3.5 and 5e have an open license. If tot read it and follow those rules you should be play. Basically forgotten realms and lore is off limits. Spell and skill names etc should be open game I believe. You just hand to read it yourself and put required legal jargon with anything you publish.
Does look like it's OGL, though I find it a bit confusing with all the legalese what aspects are actually protected. For example, I'm not entirely sure if I could make a spell called Bigby's Hand, since the proper name "Bigby" might be protected. I think I'll just play it safe and rename and reflavorize everything. I'm not particularly invested in DND 5E anyway. More just drawing inspiration from it at this point.
