'90 Plymouth Acclaim / do it yourself auto paint

The original paint has been keep peeling off. Some rust has been observed
most recently. Therefore, I decided that I am going to self-paint job. So
far, I am doing OK.
But, I wonder which one can make better result between "Spray Can" and
"Brush" Paint.
Also, I left some of tough old paint (touchup, etc.) and sprayed new paint
over. This caused slight level differences on paint surface. I wonder how
can I fix this with "Buffing" or "Sandpaper". If I can fix this slight
level difference and gloss with buffing or sandpaper, should I do that
"Before" or "After" applying Clear Coat? The other questions are as
follows:
1) How long should I wait / can I wait before applying Clear Coat?(After
applying Primer and Color Paint)
2) Can I wash my car before applying Clear Coat?
3) I park my car at parking lot / outside. What should I avoid to protect
the painted color before applying Clear Coat?
Thank you,