Well, here's my thoughts. Preschoolers really don't need much instruction. Read to them, play with them, include them in your life, and that's all that's needed. I never really did anything structured with my preschoolers aside from some Singapore Earlybird (and only because my oldest *loved* workbooks), and that was sporadic. They're both ahead in math and reading now at 5 and 7.
A baby can be a real energy suck. When I had my third, my older boys were 2 and 4. She was a relatively easy baby, but I still took a 6 month break before even *thinking* of doing anything beyond the essentials. We participated a lot in our HS group, but that was about it. Now with my 4th.. oy. He's a terrible sleeper and I'm completely exhausted. Luckily, he is pretty happy during the day so I can hold him on my lap or put him in the jumperoo while we read or do some math. But there's no way I'm doing as much as I would like, and I can't see that changing any time soon. Not until we're getting more sleep.
Anyway. My point is that if it's not too difficult for you to do things, great, but if it is, don't feel bad at all about taking a long break - especially since he's young and everything that they're 'supposed' to know at that age is easily picked up through play.