To the north of Ullapool at Handa Reserve on Handa Island, there is a puffin colony. But it is a long ride each way from Ullapool... However you will get to see puffins there - bikes are not allowed on the island - it is walkers only and you have to leave at night, but leaving your bikes at the harbour or a local B&B or campsite will not be an issue. Wild camping - you will be lucky to find somewhere dry enough to pitch at tent, some terrain is not suitable to camping and that area is one of them (and I have done masses of wild camping).
http://scottishwildlifetrust.org.uk/reserve/handa-island/ and the scenery between Ullapool and Scourie is fantastic (in good weather). It would probably add 3 days to your trip if you cycled there and back...
Getting out of Ullapool is hard work, there is only the one road (we cycled it last September) and it is a long haul up to the only road you can bale to. We did find however that we had no issues with it being the main Ullapool-Inverness road. There is also a cycle bus that covers the route I have described which I believe runs once a day every day from John O'Groats and passes through Ullapool which could be of assistance if time is tight, but I don't know much about it because we only found out about it after we had cycled out of Ullapool and ditched the idea of heading down the Torridons (mostly due to a storm and 3 days of torrential rain leaving up without a stitch of dry clothing).
I will also second or third the Callanish (or Calanais) Standing Stones on the Isle of Lewis. And if you like flora then the
Machair is worth a visit over around
Bhaltos (or Valtos) on the far west side of Lewis (my husband tells me it is pretty good on Benbecula as well, but I have not managed to get there yet) - the machair is full of orchids which are wonderful IMO. And there is plenty of wild camping on the beach and beach edge there which we have used many times over the years. The orange blob in the 2nd photo being my old tent whilst wild camping around Bhaltos a few years ago (click on the pictures for a bigger view).
There is also a broch north of the Callanish (or Calanais) standing stones which is worth visiting,
Carloway Broch which is on the road from Callenish to the Bute of Lewis.
However, the best place to get decent views of puffins are the Orkney islands and they too are well worth a visit with loads of history and wildlife. Westray was where I had my closest encounter with them - one actually landed that close to me that my 70-300mm camera lens could not focus on it because it was too close!
