I started using cork almost immediately after I started the hobby back in 2005. Very easy to work with. I haven't found any reason to seal it. As said above just primer it. Sometimes it's difficult to get into all the little nooks with spray paint, so I'll just touch up with a brush and some black paint.
Super glue has always worked well for me. I usually just super glue fig to cork. I have only had trouble, and a small amount at that, with really heavy models with small points of contact. The old metal Beastmen Minotaurs were ripped off their bases a few times (maybe 3 times in the last 8 years), but fixing it was easy.
Haven't had any trouble with plastics or the resin guys coming off.