I have also gotten conflicting advice, similar to what you have heard. I'm no expert, but I'll tell you what I ended up doing which seemed to work out pretty well, at least so far. We bought a ~100 year old home six months ago that we're just getting around to painting now, after rewiring. Most of the trim is painted with what seems to be a high gloss oil-based paint, and a much of it (especially doors and baseboards) is quite dirty. The only trim I've painted over so far is a few doors, but I'll be starting on the rest of the trim in a couple weeks. For the doors, I scraped off just whatever bits were already flaking off, then washed them really well, and then used "liquid sandpaper". If your trim is glossy you may want to use liquid sandpaper to remove the gloss. It's not a paint stripper, so you won't be left with messy globs of dissolved paint. It just removes some of the sheen so that the new layers bond to it better. Then I primed with an oil-based primer. I have used both latex and oil primers in a previous home, and the oil primers always seem to bond better. Then painted with Regal Select Semi Gloss. I haven't tried Natura, but I might... Anyway, I would recommend liquid sandpaper rather than sanding as long as the old paint is basically well-bonded to the trim, then oil-based primer, than latex paint. I'm curious what suggestions other people have..

More of an issue is the "raised-profile" the hand-prints will show!! Ideally...you'll "feather-sand" the edges of each print. Tedious....YES. Important?? Also...YES. I'd use a ~100-grit sanding sponge, then remove ALL traces of dust, then prime everything evenly. Lastly...your 2 coats of new paint! Id use a better stain-blocker than Kilz! Grab Zinssers' 123, or C2-One (much harder to find!), or...Gliddens' Gripper primer @ HD. Faron

For some reason washing surfaces before painting seems to have become unpopular and is not always done. ANY paint adheres better to a clean surface. If TSP is still available in your area (some places restrict it since it has a lot of phosphorous) it is still the best heavy duty cleaner for surfaces to be re-painted. It does take a wash and a separate rinse, but makes the surface clean to accept a new coat of paint.

I just painted a buttermilk yellow over a dark grey wall (don't ask) and for the first two walls I thought I should prime, but I still needed three coats of the yellow to cover (I paint mostly with a brush, it's only two coats with a roller). Then on the last wall I ran out of primer so used leftover beige paint... and it covered way better than the primer. I'm no expert, but my conclusion is that primer doesn't cover as well as paint. It seems to me that primer is meant to promote adhesion, not to colour things. In your situation the question is evenness, not coverage per se, so I could go over your splotches with the closest thing you have to the original wall colour. Then paint your final colour, probably two coats will do. KarinL