Congrats on the new baby!
My daughter was in in-home care (with other kids) from the time she was 4 months old and then daycare when she was around 18 months. I quit work when our second was about 4 months old, so she was a little over 2. She LOVED her daycare. She talked about her friends and her teacher, she learned a lot and had a good time there. Like you, I was worried about bringing her home full time. However, she never seemed to miss it. One day about 3 or 4 weeks after I'd been home full time she asked if she was going to school and I said she wouldn't, and that Mommy was going to stay home with her and her brother. She said "ok" and kept playing.
At the time, we couldn't afford a mother's day out program for her, but it turned out that she didn't really need it.
For that year when my daughter was 2 and my son was a newborn, outings and playdates were more for me than anyone! The social aspect of playdates and having friends wasn't really important to her until she turned 3, at which time we enrolled her in a dance class once a week and a children's bible study that also meets once a week. Those 2 days have been plenty of social stimulation for her.
In fact, play dates when she was 2 were really hard to get to. We'd leave the house always running late with her kicking and screaming because she was happy playing at home and didn't want to go anywhere. However, at 3, she looks forward to them, gets herself ready and is waiting by the door when it's time to go. I think that's just testament to all that child development stuff you read about in the magazines about parallel play, etc. They say kids aren't even capable of real social relationships until sometime after their 3rd birthday. I believe it!
The part about daycare that is good for him is the routine. They don't just have 8 hours of free play! However, you can come up with your own routine at home that will serve the same purpose for him. And you'll want to get out of the house as part of that routine, and possibly have a few playdates.
Outings and activities for the first year after my son was born were something like this:
We got together once every other week with some other moms who had kids the same age. Note: The key to happy playdates with 2 yr olds is to keep them short. An hour of free play time is PLENTY for a group of 2 yr olds. You can break up the hour with a snack.
I also got the story time schedule at our local library. We had a lot of fun there! Even the baby enjoyed it (especially when he could sit up and clap along with the songs). We went at least once a week, sometimes twice. Our library also has a lego table and train table, puzzles, and a little area where we could just sit and read books together.
The play areas at the malls are also fun, especially when it's to hot or cold to play outside.
I don't think you have anything to worry about as far as his social development. If you want to create some sort of routine and do something educational with him for part of the day, check out www.letteroftheweek.com and www.starfall.com. We aren't real regimented with the letter of the week, but if we're doing letter G, for example, I'll print out a few coloring pages, point out the letter G in books that we read, buy Grapes for the week's snack, watch Baby Galileo at video time, and use Glitter and Glue for some sort of Green craft. I sat with her for Starfall at first, but now she can use the computer by herself.
As far as a daily routine, I just make sure that meals, snacks, naps/rest times, reading books and video/TV time are at the same times every day. We fit outings, computer time, occasional crafts, free play and house work in around them on different days.
Hope all this helps!