@Austin Dame The "what if's" here are FAR too many.
I highly recommend spending some time gathering information and picking your direction then going for it. I hear unrest/indecision in this post.
If you're concerned about not selling- fix the reasons your concerned before you execute an offer on another property or accept that you are not going to get what you want. You may want to execute the sale, live short term in a rental while you search for the multi.
You can always make an offer contingent upon sale of primary residence just as you can make it contingent upon an appraisal or an inspection, but that makes your offer less appealing.
Here is the thing though- nobody knows more about what you are willing to do/capable of doing/or want to do than YOU. Therefore I highly recommend getting knowledge on your side and then making the best decision for you based on what you learn.
"Be a student,
not a follower. Don't just go do what someone says. Take interest in what someone says, then debate it, ponder it, and consider it from all angles"
- Jim Rohn