Guys, if you have any experience in web design, could you please advise me on what I can improve on the site?
When registering an account I get the message "Temp or personal mail domains are not permitted."
You have got to be out of your mind if you think I'm registering with a business email. Also gmail/outlook/etc are out because I don't use those data hoarders. If you don't want to accept valid domains, fine. Just know that close to 100% of bot account registrations on my own sites use gmail, outlook and other free email accounts. If you want to block bots, you should be wary of those free email providers. Not the other way around. You can't block the free email providers though because most people are idiots who actually use free email providers. But if you have a single domain only giving you bot accounts, block that domain. Don't carpet block anything that's not gmail/outlook/etc.
You can limit newly registered accounts with simple rules. Don't download more than x-amount, don't post links, don't add links to your profile, etc. If they break the rules they are either idiots or bots. On a couple of forums I ban all accounts that add links to their accounts. So far I've had less than a handful of false positives that were actually human but hundreds of banned bots.
One more tip for your registration form. Analyze the way people register for accounts. Most bots just spam the form in under a second. Give a human something to do on your registration form that takes a few seconds but can be done instantly by a bot. For example quote the 3rd word of a page, and then link to a simple custom page with some lorum ipsum text on your own site. Be sure to track their browser sessions across your site and have the server validation for your registration page check this actually happened. The first bot may take a while because it's learning or it's an actual human scouting your site. The bots after that will do the instant filling of the form, won't actually visit the second page and spend a second or two looking for the word. When that happens be sure to show the known bot accounts a success page even if you don't actually register their accounts and then block their IP for a week or so. If they repeat the same mistake after a while, block them forever.
Anyway, good luck with your mod site.