Maximum Retirement Contributions between Sole-Proprietor and Corporate Employer

For the first quarter I am a Sole-Proprietor (SP) and starting in April I am ending that business and will be employed by a corporation. I understand that my 401K "base" and catch-up are not to exceed $31k (over 50). My question is around other ways to fund retirement if I can exceed $77,500 total which I believe is the maximum Qualified Limit.

 

My employer will match some amount, and my SP can match some amount and I can also use After-Tax ROTH as well to meet the $77,500. Can I exceed that because two different business as matching? and if I have profit sharing from my SP business, can I also use that as well either into a retirement account or a brokerage account?

 

I've never had to deal with my own business in the same year as being employed so not too sure how all this adds up, and my limits.