All of my children have been in full time daycare from a young age (the first 2 were from 6 mths). He will be far from unstimulated. I found the interaction with the other children was great and there is so much more for them to do. The qualified staff plan their days to be interesting, fun and full of learning new and exciting things. As they get older, it becomes a great form of preperation for 'big school'.
He would have his daytime sleeps at daycare as well, so i don't think he would be more tired in the evenings - other than maybe the first few weeks while he is getting used to his new environment and carers.
My youngest is 20 weeks, I have been back to work since she was 3 weeks. Luckily I was able to take her with me until she was 12 weeks, but since then she has been at home with my mother-in-law. This has been very disheartening for me because I would love to stay at home with her, but I try to spend as much time before and after work as possible. For example, I get up that little bit earlier, so I can make sure I am able to give her her morning feed, thats OUR time. At night, I give her her bath, and bottle before she goes to bed. And most of all, I cuddle her lots.
Read a nice story before putting him to bed at night, put him in the pram and go for a stroll around the block (you'll appreciate the excercise and fresh air to), put your favourite cd on and dance around the house with him.
Your baby will appreciate any time you can spend with him, whether its games or just bathing, feeding and having a cuddle. You won't loose that bond because you go back to work, if anything, it will become stonger, because you will appreciate each other and your time together that little bit more.
Mel, mum of Joshua 8, Maddison 5, Hailey 5 mths