Straight porting will not work.
Although MIDP2.0 offers some really nice features, if you are going for device coverage, stick to MIDP1.0.
If not, use MIDP2.0
to answer your question:
drawline, fillrect.. ect. are the simplest forms of drawing.
Avoid 3d! it is not as good as one presumes (the 3d looks fine but the screen displays define how it looks and image playing Quake on a 240*320 resolution)
Memory depends on device. REALLY depends.
Check out the device listing on J2ME Polish.
Also if it says 'dynamic', write a quick midlet and test it yourself.