The scope rail will work with any weaver style ring, although the Burris Zee rings fit tight in most applications that I have mounted. Those with an adjustable clamp won't be a problem at all.
Most scope interference will be at the power ring and hammer, so most scopes will require a medium or high ring to mount without the hammer hitting. Height just depends on the scope you choose. If you happen to get one that the power rings is on the small side, or the scope is long enough that the power ring/ocular lens is behind the hammer throw, you could get away with low or medium rings.
Any ammo marketed as .223 Remington will work, but you will find that bullet weights 55gr and below will shoot best. A for sure ammo to get is the Winchester Value Pack in the white box, 45gr JHP....an excellent choice for accurate shooting in the .223 Ultra. Some have found that other heavier bullets shoot good too, but the white box ammo is a no brainer.