We have now opened a commercial services section here on the forum for registered users. If you have a Fabrik project that you wish to have someone work on for you, post it under Help Wanted. If you are an application developer and wish to earn some money helping others, post your details under Fabrik Application Developers.
Both of these are unmoderated. It will be up to both parties to work out the details and come to an agreement.
For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
As I already said, you do not want a user to be able to add elements in the frontend. Imagine "only" 1,000 users able to add "only" 5 elements each... that could result in 5,000 Fabrik elements being added. Imagine all the implications, and you should want to happily drop that idea.... the idea is the user add unlimited elements ... And allow user to add extra elements if they need to. Ofcourse this have to be donde front end ...