so he has dropped the nap completely now?
Do you use a gro-clock or similar so he knows when it is ok to get up?
Personally I would not start co-sleeping now unless I was happy with it being an ongoing thing yk? If you don't mind doing it then that's fine but if you do then it is better to stop now. He is old enough to understand bedtime and sleep rules and I am sure if you are consistent he will get the message.
It could be a bit of OT for sure if he has recently nap dropped. In that case I think it is fine to go in, reassure and then leave. Rinse, repeat. As far as routine goes if he does not tack then I would do like you are and set a reasonable BT, say 7pm and stick with it.