First off, you are better off asking questions at the new
official forums at Desura. That said...
1) Remote site searching spells are the height of inefficiency. It is most of the time a massive waste of both gems and mage time, because you need eight mages to search all eight paths. Acashic Record is way too expensive unless you have set site frequency to something ridiculously high.
In order to maximize your efficiency in site searching, read
the site searching guide.
The long and short of it is that an across the board level 2 search finds 85% of available sites and a level 1 search finds 50%. So the best searchers are mages who have level 2-3 in two or more magic paths simultaneously. If you have a mage with three paths at level 2, they are excellent.
Gems should also be used to forge items to boost your mages, thugs and super combatants.
2) There is no one-size-fits-all answer to this. The rule of thumb is that you should recruit a mage every turn in every fort where you can and the ones who are not site searching (you need small parties for this) should be researching if not required in combat. A research pool of 130 points per turn is actually not a whole lot after a while in the game.
3) Branching out should be done by taking magics on your pretender that your nation doesn't have and doing proper site searching so you can snag any independent mages from good sites. Nature searches are especially important for this since with luck you can get excellent sites that get you high nature plus elements and astral. There are practically entire guides for this.
4) The AI does not know how to handle LA Ermor (either as an enemy or very well under its own control). As far as scales go, turmoil + luck is a crap combo. For Ermor it's the right one, though many events also have other scale requirements, so you can't bank on those big treasure events. The dominion of LA Ermor will kill your population anyway, even if you had growth 3, so you can't avoid that and need to plan strategies for it. It's not a nation for beginners, really.