Hiya, when my ds started nursery 4 years ago (he's still there) there were about 4 cots in the main baby play room. He went full-time, and had a designated cot which he would sleep in. Ds only used to sleep for about half an hour at a time in the main baby room, so shorter than he slept at home, but it never bothered him, he just had more naps !! He moved up to the next room at 15 months and then slept in a darkened room on a mat, he would then sleep for over an hour but only once a day.
I then had dd1 and she started at the same nursery at 10 months. By then they had had an extension and they had a separate dark sleep room with designated cots for the children. Dd1 used to sleep for much longer in there than ds had done previously, but it didn't make much difference to her overall happiness - they've both loved nursery !! By then I was only doing 4 mornings, rather than full-time (and 4/5 evenings in a different job though).
I also now have dd2 at nursery (ouch, the fees for three !) and she tends to sleep in the baby swing for an hour and a half in the main room.
So, they have all been different but they've all been very happy and the sleeping arrangements have made no difference (I think the staff have it easier with a separate room as the children sleep longer !) I would make my choice based on gut feeling/staff turnover/outside play area/hygiene etc etc and would not worry about cots in main room or separate. Almost all children will sleep on mats after about 15 months ish, and as you are probably talking about the next 3+ years at nursery, I wouldn't worry about the next 5 months......
Good luck choosing