Your problems have absolutely nothing to do with the fact that you are using a repack. I'd suggest you to look at some MySQL guides and to some guides for MySQL editor you are using. Tables like item_template contain dozens of thousands of rows and of course, MySQL server won't show you all of them at once, that would be huge slap across performance. You need to specify which entries you want to browse by setting limits and/or filters and/or sorts. If you have absolutely no clue wth am I talking about, like I said, take a look at some MySQL tutorials (not here, I mean, MySQL in general) first and when you can perform some basic DB tasks, you won't have problems like this.
About database stuff:
1. open
https://trinitycore.atlassian.net/wiki2. enter table name into search window
3. open your table's documenttion to see, what is there for what. You should be able to figure out pretty much on your own with this documentation.
For DBCs, the same, just different wiki:
https://wowdev.wiki/Main_PageHow to create a custom patch and edit DBCs and stuff like that is all described in getting started tutorials:
viewforum.php?f=78http://www.model-changing.net/tutorials ... -beginner/I could describe to you just to make particular things you want to do happen, but that wouldn't teach you anything and you would be left unable to perform another tasks on your own. Which is why I've pretty much thrown a documentation and set of tutorials and guides on you. If you have any questions, feel free to ask them though.