On my first play through and while the combat takes a little getting used to I'm really liking the game so far.
Any advice on:
1) Should I sell everything?
2) Should I dismantle everything, seems expensive?
3) Should I be buying equipment?
4) Any advice on skills? It seems a little overwhelming with all of the choices. So far I've done fast attack and the increased witcher mind trick thing.
5) I accidentally skipped the Gwent tutorial. I don't really have an interest in playing, is this ok? Is it a mistake not to play?
1) Only sell items that have weight. Mainly enemy weapons, armor, and stuff like pelts, plates and things in the misc category. The rest (alchemy items, jewels, etc) is weightless and potentially useful later for crafting, so try to keep it. If you're in a bind you can sell an emerald, or a ruby or something or something for some spare gold, but try to keep all the crafting supplies at least until you know what you need. Also don't forget to visit the bank to convert your foreign coins - can really add up.
2) Dismantling is only useful if you have runestones equipped in a sword (destroys the sword but keeps the stones), or if you need a certain material and you can get it by dismantling. Dismantling can also make monster guts "generic" - i.e; dismantle a "drowner brain" into "monster brain" if you need one for a recipe. Can come in handy but no need to dismantle everything at all.
3) No, not really. You should be able to get decent items from quest and looting, until you find plans to craft the various Witcher armors and swords - those are generally the way to go. Plus the quests to find the plans are surprisingly cool and interesting.
4) The mind trick is a good one, yes. Sword builds are solid and fun - try to get whirl. It allows you to simply hold down the light attack button to do a nearly endless whirling onslaught. Also the skill that reduces damage from dodged attack by 100% is very good too.
5) Gwent is fun but 100% optional. Try it a couple times but it basically never comes into play in the main game. The tournament quests are cool though, but its mostly a self contained thing. You don't really miss much by not playing.