Just don't lug the engine. Cruising at a low rpm is fine, as long as the engine doesn't lug, shake, rattle and roll.
The rpm you shift at doesn't matter as far as smoothness of shifting goes. It just takes practice making quick and smooth shifts-not power shifting.
Don't take the risk of downshifting into too low a gear. After all, what's the point? Are you planning to race on a road course? I doubt it.