Should I have wallpaper removed or painted over?

Details:
- average size bedroom
- inside 1920s home in beautiful condition
- half of the room's walls are lath and plaster, half are sheetrock
- in 1998 all layers of wallpaper/paint were removed, walls repaired, wallpaper applied
- the wallpaper was applied by a professional, still in perfect quality
- so we're certain there is only one layer of wallpaper
- there are two small wall cracks which have caused the paper to tear

Goals:
- paint 3 walls
- apply new wallpaper on one wall

I was thinking painting over the walls would save money and time, and because I read that taking down the paper can sometimes cause problems. What would you recommend?

If you'd paint over the wallpaper, do you recommend an oil based primer for painting over wallpaper?
Any special paint?

Thanks!