LoopyLeo wrote:[...] I'm wondering how many skills one should train at a time,
Training one skill at a time is strictly best (as long as that's the most useful skill to train of course). Many players don't do this because it can be a bit tedious, as it requires regular checking of the skill screen and making changes as required. I usually do that until my character feels strong.
LoopyLeo wrote: especially when playing a mage character.
There's no real training strategy difference between a 'mage' character and a 'fighter'. Both need to train some offense in the beginning, then get some defences, then get more offence and some utility, and so on. Mage backgrounds (IE, FE, Su, etc.) often start with some really strong spells in their book. It's usually most important to get those spells memorised and to a low fail rate. Fire Elementalists benefit enormously from Conjure Flame for example.
Please note that you do
not need to race to get all the spells in the book castable. Trying to go straight for Fireball is usually a mistake, for example.
In order to get a spell to the desired fail rate it is best to split XP fairly evenly between all the involved skills. For Conjure Flame that is Fire and Conjurations. For other spells it may only be a single spell school. Please note that XP is not the same as skill levels. The skill screen can show you the relative XP cost to get to the next whole level of a skill. Try to keep those numbers similar. Picking Int for stat choices will often help to get the fail rate down and the spell power up. Once you have a reliable way to kill enemies, add some defences like training fighting and dodging.
LoopyLeo wrote: Fighters I generally leave on weapon, fighting and shield, with a focus on weapon skill -- is that "right"? It seems odd trying to get to min-delay whilst maintaining a shield penalty :/
Generally speaking, training shields in the early game is a mistake. I mainly split my XP between weapon skill and fighting in the beginning, with characters that kill in melee combat. I put an emphasis on weapon skill. You don't need to train to min-delay immediately, but it should be a medium term goal. Once you find a decent armour, like chain or plate, train a little armour skill to pick up a cheap point of AC or two. If you can pay enough attention, then you can train armour and dodging precisely to the point where you get an extra EV or AC, then decide whether to continue training, or to change to something else.
LoopyLeo wrote:Then on my mage characters is where I have the biggest trouble -- I've generally been leaving on fighting/dodging (I generally play squishier casters), whilst also training element school AND spellcasting -- I always read people saying not to bother training spellcasting that much, but I find I personally can't seem to survive without the extra MP.[...]
See above, train to get the good spells of the background, like Conjure Flame. I would focus on that first and train fighting/dodging a little later. Finally, I usually only train spellcasting for extra spell levels, or if it is much lower than my main magic skills (like when it requires only a quarter of the XP to raise to the next level).
There can be multiple reasons for running out of MP. Training your damage spell skills (like conjurations/fire) will increase their damage and make them more MP efficient. It also increases your damage per turn. FInally it also increases your chance to hit with some spells, or your chance to overcome enemy magic resistance with other spells.
It is often best to fight enemies one at a time, partly because MP is quite limited in the beginning of the game. Once attracting an enemy, pull back to a safer area, then kill it there, wait to regenerate MP, then look for the next enemy. Many book backgrounds start with some stealth making this relatively straightforward.