Btdt moms- speech delay/Second baby

I have a 16 mo old son. He is such a wonderful little man who has always been extremely laid back. He has also always been on the late side of his milestones. I think this is a combination of his personality as well as just being on the "slower" side to progress. Which I know can be normal for boys. He didn't crawl until 10 months, walk until 15, and he speaks no words. He also doesn't really try to communicate with us besides tantrums (probably because he is frustrated). for example he doesn't really point much either, although he is getting better at that. He is very happy overall but very independent and fine with doing his own thing and observing for the most part.
Long story short, we have started him in an early intervention therapy biweekly working with a developmental therapist. We are working on things like eye contact, mimicking sounds, sign language. I've seen a lot of progress in him which I know is the important part. My husband didn't talk until he was 3.5 so I think my son is just going to take his time as well. 
He will turn 2 in February, this baby is due in March. We are so excited but i'm starting to panic that we should have waited longer until my son was more "acclimated". I'm worried that a big change like this may delay him more. And that he won't have the words or capability to communicate with us how he is feeling. 
I'd love any input from any moms who have possibly been in a similar scenario or just anyone who's nervous about spacing at 2 years apart! And I feel guilty for even saying I wish we'd waited. Just feeling kinda overwhelmed. Thanks girls.