How to paint / repaint / touch up the paint on garage door / garage door frame and gutters?

Question:This is three similar questions rolled into one.
1- Garage door is metal currently white. No rust just one or two spots with some stain. Can I just directly spray paint on top of the current coat?
2- Garage frame is wood. No peeling paint. Again, looks good except for a few spots of dirt and grease? Can I just paint on top or do I need to sand down?
3- Gutters with Soffit looks fine, some moldiness. Will pressure washing followed by spray of paint work?

Answers:
1)rub your hand on the garage door to see if it is chalking(color comes off on your hand),if it is then your need to wash it with tri sodium phosphate(tsp) to remove the chalking paint. However if you do that than you will cause ugly streaks next to the spot in question,and so on and so on. Chalking paint will not allow the new paint to bond and will peel. So your choices are live with the stain or repaint the entire garage door.
2)the same applies to the frame ,except for a very glossy surface needs to be sanded to a dull appearance for proper adhesion of the new paint.
3)again ,the same applies including the contaminates on the surface need to be removed. The stains maybe from the roof shingles, in which case you might not be able to remove the stain.
NOW: touching up with anything but the very same coating will in most cases be as unsightly as the dirt and stains, and using the very same coating may not match due to fading.
So if you are touching up for protection of the subsurface you are getting what your after. If you are touching up for appearance then you will no doubt waste your time.
Call a painter for an estimate and run these very questions by him. call a painter that has at least 5 years of residential repaint experience.