Does categories ID link to Media Item Category ID properly? Only you would know if the fields are meant to be connected.

Limiting a result to a specific media type is the adding of criteria for that specific type (either by name or category ID).

On the second, if you have 1 table that has the title, that should be sufficient, because you can always link tables to get corresponding results.

If you set up relationships, which is little beyond where you are right now, you can specify that X from Table A = X From Table B and they kind of "link up" automatically behind the scenes...

If I have time later I will do some work and set up relationships and table queries that you might find useful to learn from.