Yes thanks. What is "convert increase attempts" on my mage?
I'd advise against it. Spell Points are hard to come by, experiences are not.
Well right after I clicked "no" on "convert increase attempts", a new window opened asking me "convert 10 attempts on magic skills to astral points?". How the fuck do I know I didn't even start my adventure yet or look at the skill sheet man.
Also what would be a good spell school to focus on?
1. Less attempts to acquire more spells—or more powerful version of spells—and instead have more Astral Points. ----> I'd also say no that. Especially for first playthrough.
2. For Magicians: definitely Combat. Other must-have schools are are Healing (self-translating) and Movement (will save you a lot of pain during some adventure situations). Also don't forget you can have other spell-casters in your party, so don't spread your talents too thin. Specialize in only a few spells per character at first, then you'll see what's what.
On Clairvoyance and Transmutation: The former can provide some additional info about objects, creatures, situations, NPC's thoughts etc.—that's good because the game is kind of untoward with information in general—as you yourself have already seen during the character creation :D The latter has got some nice buffs, if you are into this sort of thing.
Other than that, I think it's purely optional. You could even go without Combat magic, and have, idk, a Skeletons and Demons summoning Dark-Wizard-Lord :D but I've always felt more inclined towards naturally damaging Wizards (sorry, Magicians here), so I've never tried other schools all that much.
Last but not least, Blade of Destiny is one of those games in which you can brick progress. It's rare, but it can happen. So, save into different files every now and then. I hope it's not much of a spoiler if I tell you that one of those moments can come if you don't have Melt the Solid or Freeze the Soft spells from the Transmutation school upgraded to at least few levels. Sorry, I don't remember which one was it in particular.