Hi, for starters - dont worry about starter skills, skillbooks are later hard to acquire and you wont miss anything!
Respec is definitely possible since start of act2, and its free for every character - so dont worry so much.
And for party - I actually like mixed team, and even mixed characters, atleast a little bit! I like my warfare with three geo spells, I like my mage with necro spells so he can deal physical and magical damage, I like my ranger with pyro for buffs and occasional fire spell light up some surface and so on.. just dont overdo it, but atleast basic support spells should have most of your companions
