I use the 3000. Got enough grunt, but can run at low speed.
Do not get the chargeable one, it runs out of charge very quickly and takes to long to recharge.
All the good rotary tools are similar, but the dremel has user changeable bushes that do not require you to disassemble it to replace.
The 3000 has 8 speeds, whilst the 4000 has variable. For kit work I normally only go to speed 3/ You want slow else its to easy to overwork/ sand /cut an area
The two most important and useful accessories are the stand and the chuck. ( saves changing col lets and is quick release ( fits .4mm drill bits up to 4mm pluss all the sanding cutting bits etc)
Go fora kit box as you normally get the extension with it and they sell cheaper near xmas / fathers day.