Kedushat Beit Knesset of a Rented Building

Clients of mine want to rent out a building that has served for a family business to a religious group, who will use part of it as a shul. They are concerned that if things do not work out, they will get back control of the building with some of it having the restrictions of a shul, which would restrict their use of it. Is this a problem, and if so what can be done to obviate the problem?

Sefarim under Seats

In our shul, the seats have drawers underneath them to store chumashim, siddurim, etc. Thus, we sit over these books. Is that allowed?

Donating a Sefer Torah to a Shul

People who own sifrei Torah often lend them to a shul. Is there any reason they cannot donate them (which can get them a tax credit)?

Lighting a Candle When the Ner Tamid Is Out?