Hi Keenan,
Welcome to the forums.
Provided the voltage and cell count of the pack are the same as the original, you can put a bigger capacity pack on. The limiting factor is the weight of it which put more stress on the motor(s) to fly. I have an 1600 pack on my B47 twister which works fine considering it came with an 850 pack out of the box. As far as a charger goes, it depends if you intend to go on to flying bigger helis in the future. If thats the case buy the most flexible charger you can afford, the trouble is it will cost you more than the heli did. The advantage is that if you buy a trex 600, then you would be able to charge its pack without getting another charger. If its any help, Ive got a Robbe Power Peak Ultimate Li which can charge anything up to a 4 cell lipo.
Drift at liftoff is normal and to be expected and it is usually to the left due to the direction that the blades travel in. I wouldnt try to "trim" it out since you will stuff up the helis flying trim and you need to take it out to maintian a hover once your bird is airborne. Instead, you should compensate by putting in small ammounts of roll and pitch. If once its in the hover it is consistently moving forward and you need to HOLD in roll or pitch, then you should trim but if its just a dab of stick and she straighens out, then thats normal. To answer the stability question... unlike planes, helis need 100% of your attention 100% of the time, there is NO let up and you really need to be flying them from the second the blades start to generate lift... ie before they get off the ground. A well set up and trimmed heli will hover hands off for a few seconds but I guarantee that she will start doing her own thing and will need correction within about 8 seconds. The only exception to this Ive seen is the contra rotating blade type machines which if they have a big enough space, will hover forever (but they will still drift around).
When they are in forward flight, helis behave pretty much the same as planes with the exception that they tend to climb in turns.
Hope this helps.... Azzy
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