1. i don't have a mic, is that okay
2.  will my skills in the demo transfer over
3. should i bother with expansions

1. It's fine. You'll probably miss out on talking to people and strategizing but it's fine.
2. Don't think so. Never played the demo so I'm really not sure. I'm guessing no.
3. I'm thinking yes. Haven't played WarHawk in a while but I think that expansions are needed to join servers with expansion maps. But I have been wrong.

1. if your playing with people you know or want to be at all tactical you need a mic, think battlefield without the preset commands
2 not sure
3 All the expansions are alright however i dont think anyone actually plays them vey much

not having a mic is all ways bad in a mutliplayer game.
if you mean what you've learnt on your own then yeah they would carry over.
the expansions are pretty much a requirement if you wanna play alot of games.

My advice would be that you should have gotten into the game after launch the game is strictly now warhawks people rarely get into tanks or go on foot because after so many updates the warhawks have become inanely over powered and you will often die many times upon arrival in a server and spawn.

1.  Unless you have friends playing mics arent a big deal.  Every game i have ever been in less than half of the people have mics.

2.  It will probably be a lil harder than the demo.

3.  A meaningful number of matches use the new maps.  Their good so get them all in the bundle.