I have seen characters with personalised items and weapons and was wondering whats the rules concerning these? are these rewards or just requestable to add to the roleplay of characters, if they are requestable and have magical enhancements. whats considered a balanced item? thanks in advance

If you want a personalized item that fits your backstory in some way, you can make a request. Generally the only items appropriate for this would be something useless and even then you'd need to find a DM with time and interest. I'll gladly setname an item for players IG (changing a mundane item's name) personally, but I'm reluctant to go through the trouble of loading up the toolset/making an item/saving it on a character file/logging that in as a DM for a particular piece of background loot unless there's an excellent reason for it.

Otherwise, there's all kinds of custom magic loot out there. Some of it is found randomly on DM quests, a lot of loot is made custom for a character because the RP of the character really seemed good and the DMs want to reward that character. Of course, if your character doesn't have any custom loot you shouldn't interpret that to mean that the DMs don't like your PC -- we simply don't have time to get something to everyone deserving.