Soffit vents can be painted as long as they are appropriately primed based on their existing finish.
With either gable vents, soffit vents or ridge vents. The more the better
No, but they all should have.
Most soffit material is now made with a continuous 3" wide vent.
The vents allow the loft space to breath. By blocking it can cause damp air to accumilate and thereafter you have condensation damp and mould.
Clean via power spray, scrape and sand, prime and paint.
WHICH VENT If you're talking plumbing roof vents or soffit or ridge attic air vents; absolutely not!! I can't thing of a single vent that would be opened and closed at will.
Soffit vents are located n the soffits, which are the horizontal surface between the top of the wall and the edge of the roofline along the bottom line of the roof. Usually the same roof edge line where you may have gutters installed. These vents allow air to flow into your attic to provide ventilation which may then flow out the ridge vent or gable end vents. You can see an image here: http://www.cornerhardware.com/howto/images/ht076_2.jpg
It is recommended that you have both intake vents and exhaust vents. Most do it yourself sites recommend soffit vents for the intakes. Exhaust vents vary in both type and cost. For smaller houses the most recommended type is a ridge vent system. The number you will need depends on the square footage of your attic.
Soffit
Make sure none get into the vents, and use plastic safe paint.
the roof is required to have venting (size) based upon the square footage of the ceiling area
The soffit of a pipe refers to the underside or bottom of the pipe. It is the part of the pipe that is facing downwards or towards the ground. The soffit can be important for ventilation and drainage purposes, and it is often covered with a soffit vent to allow air to flow through.