Trim: when youre new to the game (especially if you dont have much prior experience with realistic flight sims), i recommend using combat trim. In OPTIONS > PREFERENCES > Flight on your clipboard, you can enable "Auto Combat Trim"... this will keep you in Combat trim automatically. But you can always toggle combat trim manually by pressing default key (CTRL X) if you prefer.
For your speed/RPM issue. If you are in a plane that has WEP (most fighters, for example the Spits or the P51), you should be able to toggle extra power with P when youre at full throttle.
Or you can open E6B on your clipboard. All the engine settings (for Cruise, Normal or Military Power etc) are listed there, and you can compare with your gauges in cockpit.
If you have a throttle lever on your Joystick, keyboard commads are switched off. Make sure you calibrated throttle lever as well.
The plane going down/sideways is probably engine torque effects, which are more noticable at lower speeds. When on the ground, use rudder to counteract. In the air, its best to try and level off to gain speed. Avoid any hard maneuvering untill youve gained some speed. Were talking WW2 prop planes here, not MIG29s
- give them some time to accellerate. Listen to the buzzing sound, its your stall warning: youre about to loose control... get more speed/avoid hard maneuvers. Remember, Always be gentle with that stick of yours!
On the use of flaps: they will add lift (ie nose high tendency), but they also add a lot of drag. At the beginning, while you get a feeling on how to fly the planes in AH, i wouldnt worry about them except when landing. You dont really need them.
If you want to stay offline for the time being, i recommend you get yourself an easy to handle plane like a Spit Mk9 or a Hurricane Mk2 and get a feel for the Flight Model and try your aim on the drones.
But keep in mind you have a two week free trial for the online arenas. You can always come by the Training Arena and work with a member of the Trainer Corps. Also, usually there are longtime players online that can help you with getting started as well.
Check out
http://www.netaces.org for hint and tips and writeups on gameplay, flying, combat tactics and a lot more.