My gaming and GMing style is to be in-character as much as possible, but not more than people are comfortable with. The number one rule is always err on the side of fun, unless it will create an obvious problem for later, and that means, for me, that if people are more comfortable speaking in character, let them, and if not, that's fine too.
I recommend a screen. Especially when you're getting used to the rules, you'll want to fudge rolls from time to time. I fudge rolls mostly in order to avoid killing a character too quickly (I GM Savage Worlds, where a lucky roll can one-shot anyone), or sometimes to make sure my big bad gets at least *one* use of his cool power. As I'm getting used to the rules, howevever, I'm fudging less and less.
Meta-gaming isn't even a thing, for me. That's probably a topic for another discussion, but IMHO, the meta-game is often as fun as the game, and there's nothing wrong with enjoying it on multiple levels. I avoid keeping information secret for two reasons: 1) the other PCs are going to find out eventually, so why make it necessary to share twice? and 2) if players are trying to keep secrets from eachother, there is likely a problem. The only time I would keep information to specific players only is if I think the surprise will be more fun. (I had a GM who used to take a player into another room and info-dump on them. Everyone was bored during this, and the player usually ended up just dumping it all on the table as soon as he got back in the room. This was a huge waste of time. We're all experienced role-players. We can act on in-character knowledge. Let's just keep it going...)
3D terrain is cool. Tac-tiles look awesome, but you're right- they're spendy. Honestly, a plain roll-up mat has always been fine for me.
I've been a player in the Kingmaker AP for a while now. We're all enjoying it. I find the kingdom-building rules to be interesting, but it's a side-game I'm less interested in than the actual character-level RPing. I heard the newer rules are better.
Make sure the players are all on the same page as far as what the game is concerned. I recommend "The Same-Page Tool" : http://bankuei.wordpress.com/2010/03/27/the-same-page-tool/
Make sure there is some level of party cohesion. Most players can't handle a group working at cross-purposes. I recommend using the "Group Template" from the "Fear the Boot" podcast: http://www.feartheboot.com/ftb/wp-content/uploads/resources/2_GroupTemplate.pdf
Stuff I've learned from bad GMs:
As a GM, don't plan too much. Don't ever bank on your players following any path. This is *not* like writing a story, from your perspective. Instead, be ready to create the story around where your characters go and what they choose to do. This won't be easy for a beginning GM, so be patient and forgive yourself if it doesn't go well. You'll realize quickly what I'm talking about. Make sure you have a clear understanding of your NPCs and Villain's motivations, and an idea of what exists just outside your party's location, and doing this will be easier.
If your players decide to go easy on you, they'll be merciful and bite down on your plot hooks and not stray too far from your plans, but don't ever force them. Dungeon crawls are a good place to start for this. If everyone is cool with that, it'll be a good way to get a feel for the rules and the group before you start doing more improv.
Remember it's not you vs. them. You're all grown ups, and you don't need to be antagonistic (only your npc villains need to be). Assume they're not going to try to screw you over, and you aren't trying to do the same for them. If you display patience and flexibility, you'll hopefully get the same from them. If you make a bad call and a player suffers for it, then there's nothing wrong with re-writing history to undo it or somehing else to make up for it. Also, don't worry too much about being too generous as long as you don't think your players are going to take advantage of this. If they are- they're missing the part where this is a game, and should be about fun.