The following is only my opinion, and it's worth what you paid for it.
Definitely get a stick soonest, don't waste you're time flying with a mouse. Any cheap stick is 16 times better than using a mouse. Inexpensive sticks have already been recommended, so if you have the money for a permanent, quality stick here's the low down as I see it.
Very best for quality, reliability and long life is CH sticks (stick and throttle units, and rudder pedals, if you want). But they are initially very expensive, something in the $300+ range, I think, but very economical in the long term as they are solidly built and seem to last.
Thrustmaster is supposed to have a top quality stick or two, but I really don't know anything about them.
Next are the Saitek sticks, which are very popular, as mentioned before. The new X52 Pro (separate joystick and throttle units, rudder pedals additional) being their top of the line at between $155-$200 depending on where you buy. The Pro has pretty much an identical layout as the original X52 (around $100-120 and sure to drop with the new X52 out), and it seems a little sturdier and supposedly more reliable long term (we'll see, as I just bought one). Either of these two sticks provide a massive amount of button and trigger controls (as does the CH). Additionally, many people use the X45 by Saitek as well.
Being able to map critical flight controls to your stick is an advantage over a keyboard unless you are very, very proficient in blindly hitting keys during a fight.
I would next suggest if you don't already have one, get a microphone for radio communication. A cheap $10-15 mic works just fine. You plug it in, see if you can record and playback in Windows and you're good to go in AH. Communication is the most limiting and critical factor in this game if you wish to learn and train with someone, and engage in any coordinated combat with others. There are a very few who can communicate efficiently via keyboard in the game, but it's still too slow in a hot furball.
Finally, make sure your views are set up properly. Ask a vet if you don't know if they are. Cardinal rule of ACM is never, ever lose sight of your enemy, and if you don't have them set up correctly and position you're pilot in the cockpit just where you want him, you will die more often than necessary by at least double.
Hope this is helpful.
