IMO, the answers to your first two questions are:
Yes, it is acceptable - I currently use RCA to XLR adapters because my CD player is single-ended only and my preamp is balanced only; and It Depends - as any sonic compromise resulting from the use of adapters may not be audible, depending on the quality of your equipment, synergy of the system, room setup, and (of course) your hearing.
I upgraded my preamp and had to go with adapters. I started with generic Chinese-made adapters while I considered my long-term plans. Some people have/will recommend that you have a custom RCA to XLR cable made. I considered this, but opted to buy high-quality adapters as I anticipate upgrading my CD player this year (and then I will go with a balanced cable and pitch the adapters).
As to your last question:
There are a few good quality adapters available. As previously mentioned, Purist and Cardas produce some. I was told that ARC also sells them. I bought a pair of the Cardas adapters from A-gon member Drubrew.
After they settled in they sounded much better than the generic ones I had originally.