I went straight from a cheapo 3ch to a 6ch heli
Its doable but not without incidents!! Steep learning curve aint a strong enough word.
Downside to a 4ch is boredom factor. Once you go 6ch I doubt the 4ch will get flown much, money spent on one of them could be spent on your 6ch beginner crashes.
Have a look at all the Eflite Blade series cheap ish, parts everywhere nd they will deffo have one perfect for you!.Im only sugesting Eflite as they are cheaper than Align.
Jay