We have done multiple add-ons, through Disney (which is fastest) and resellers (also easy, but takes about 2 months total). It might be worth a call to Disney to see if they have any Vero points (maybe from a foreclosure?)
As long as you get add-on points with the same use year as your original contract you will have no problems. I don't even know the difference -- it's as if we had bought one big contract at the beginning. If you buy less than 150 points, Disney will only sell you the same use year as your original contract, I believe. If you buy resale your life will be lots simpler if you look for a contract with the same use year.
Closing costs with resellers will probably be at least $375 and more like $500. You could negotiate for the seller to pay these, though many buyers seem to negotiate on price and pay closing themselves to discourage Disney from taking the contract under ROFR. We have worked with 3 different resale agencies and all have been great. Timeshare Store (see link at top of page) seems to always have the most inventory, but you can call any of the resellers, tell them what you want, and they will contact you when something comes in.
Good luck! Maybe you'll find something with banked points!