Well Lets see.............
1) A de-priming die is not necessary. I have one cause I like to de-prime my fired cases before tumble cleaning them - but it is NOT a requirement.
2) A case trimmer WILL be required at some point - especially if you full length resize. Resizing stretches the brass toward the case mouth and eventually, your cases will get too long & not chamber if they aren't trimmed. The little Lee trimmer that you can use by hand is all you would need for the time being..........it costs about $6 for the trimmer and case holder.
3-4) A de-burring & chamfering tool will be needed for brass that has been trimmed to keep the mouth open to accept bullets.
5) Your Lee Die set should have a case holder in it - it will be needed because it holds the case for the sizing, priming, & bullet loading processes.

As far as universality is concerned, a de-bur/chamfer tool is, as well as the de-priming die. Case holders can be used for different cases in the same family.......a case holder for a .308Win also is good for .243 and any other case with the same head dimensions - even for .45ACP. Case trimmers are usually universal, but you have to have a piece for each bore caliber you trim................unless you go with the little Lee trimmer - that is a case-specific design.