Selling $50s at 93%, payment with Zelle/QP
As of combining with coupons/eBucks - yes it works
I'm not very active on eBay now (they exclude GCs from much of what I buy), but the stated limit is 8 cards per transaction. In the past it was softly enforced - I'd be able to use 9, 10, 11 etc - until it would crash. Have no idea how is it enforced nowadays, would appreciate the recent experience.