1) Lld only goes up to level 30
2) No, upgrading a shaeled ravenclaw makes it rlvl 34, whereas upgrading a unsocketed ravenclaw, and then shaeling it, makes it rlvl 28
When you upgrade an item in D2, it adds 5 required levels to its new maximum required level, based on what has the highest, the item mods (unique level), the base item, and the socketed items
when it is not socketed, the level becomes the base of the cedar bow (23) and adds 5 to get 28, and when you shael it, it becomes 29 (level of shael)
when it is already shaeled first, it reads its rlvl as 29, and makes it now 34, even if you remove the socket; its possible to get a required level 74 biggins bonnet war hat
So always upgrade the item before you socket it
3) Upgrading raven claw makes it possible to strength glitch the bow so that its arrows are invisible. A normal longbow needs 22/19 requirements, and a pally has 25/20 base stats. It is impossible to strength glitch and unupgraded raven claw on a paladin. You need to upgrade it and use +stat charms to reach its requirements in order to make your arrows invisible. And this is too good of a bonus for the build to pass up
4) Holy shock auradins do indeed work, but usually stick with zeal; they don't have an arrow delivery like a holy fire paladin does because lightning damage does not apply to exploding arrows, and there is no similar glitch for that. So they are almost always just zealots/chargers for LLD, and you can find some nice guides for them
hope that helps answer some of your questions