Mixed Media Painting and preparing canvas/board.?

[RadicalReason]

I wish to use emulsions, possibly acrylic spray paints, and acrylics on a ground of multi purpose filler for texture and mark making. My question is:

For the paintings longevity what treatments do I need to give to the canvas? i.e primers etc. I will be using filler on canvas - willthis be ok?

What varnishes should I use?

All and any help will be appreciated. I want to fire straight ahead with ideas and processess but I realise that having a grounding in the effects of materials and time will help the pieces last for a long time.