By default Gitlab has a limit of 10 projects, but you can change this if you go to:
Now you have to look for the Account and Limit Settings section, here's a screenshot:
I changed the default limit to 100 projects. That should work!
Regarding your second question:
Gitlab is developed in ruby on rails. You can change the appearance of the application if you go to:
But if you want to make changes in the code I would highly recommend you to use the https://forum.gitlab.com/. I think they will help you a lot.
Thanks and best regards!!