That’s an impressive DIY list! Your little boy is absolutely adorable.
I don’t think it would be weird to invite your friend. I’d perhaps pop her a message via fb saying your invite is in the post - I know we don’t see each other as much but I’d still love you to share our day. No pressure though as I know it’s a long way to come! Or something along those lines in case you think she might think it’s very out of the blue. As numbers shift you can play around with it and if your husband already has more numbers then definitely invite on your side first! Any further declines can go on an individual basis of who is closer etc.