As to ammo, mine likes Wolf MT the best. Wolf can be a little pricey if you do a lot of shooting. As with any rifle, you'd do well to experiment with different brands. You may get really lucky and have a rifle that shoots the $.90 a box ammo.
Your .22 Millet rings won't sit down directly on the receiver, but will still provide plenty of holding power for rimfire shooting. I used them for a long time with no problems. The Millet Angle-Locs designed for the 11mm dovetail are fairly pricey, so I'd use the ones you have.
What size scope are you thinking of using?