Olaf the Stout said:
So what size brushes do I need to get? And what about brush conditioner or cleaner? What products would you recommend?
The gold standard used to be the Winsor & Newton Series 7 or Series 7 Miniature Kolinsky sable round. I've been told that W&N no longer has the same brush makers and their quality has dropped. I use (and am quite happy with) the
Da Vinci Maestro Kolinsky Sable Round Series 10. (The link is to Dick Blick, which has excellent service and very good prices.)
Good Kolinsky Sable brushes are expensive (relative to other brushes), but they are
absolutely worth the difference in price. I regret the years I wasn't willing to spend the money for a good brush.
Brush size is a personal issue, but I do nearly all my painting with a #2 brush. The relatively large brush size allows the brush to hold enough paint to keep from drying out immediately (a significant problem with 000 and smaller brushes). And one of the reasons to pay for a good brush is that the point is (and remains) so very good. That da Vinci #2 has a better point than most 10/0 brushes I've used, even after using it for months.
I do keep a #0 and a #000 brush around, but I hardly ever even get them out of my brush holder.
Edited to add:
I use
The Masters Brush Cleaner and Preserver for general brush cleaning. When brushes get really gunky (or after a few months), I use
Winsor & Newton Brush Cleaner and Restorer. Any really basic hair conditioner works fine to recondition a brush after a thorough cleaning.