I thought Spell focus only affects saving throw DCs...
You are correct. Spell focus feats in abjuration will not help your dispels. They will raise the DCs of spells in that school that require a saving throw, but there aren't many of those of consequence in abjuration. Dismissal and Banishment both benefit from the feat, but those spells would likely only be useful a handful of times in the OC. In my opinion, Spell focus in abjuration would not be a good use of a feat.
Typically, people take spell focus in evocation to increase the average damage of many spells that allow a saving throw (Firebrand, Cone of Cold, Sunburst, Meteor Swarm, etc.) and in necromancy, to increase the effectiveness of instant death spells and necromancy spells that cause damage (typically Negative Energy Burst and Horrid Wilting) and maybe Fear for crowd control. If the module has very few creatures with immunity to mind effects, then some people like to focus in enchantment spells. IMO, the former two are better choices for the OC.
Spell penetration isn't necessary, but can help against some foes in the OC. There may be a few dragons with notable SR and a planar beast or two as well. Many people who are playing pure casters don't take it because their spell penetration is so high just due to high caster level at level 40. But in the OC, that isn't relevant as the PC will be level 15 to 17 when he encounters some creatures with SR in the twenties.It may still be advisable to employ breach spells to lower those opponents' SR, of course. But, the spell pen feats will allow more spells to hit if one runs low on breaches or prefers to cast extra spells while hasted instead of using breaches from scrolls. It's partly a play style thing. Some players will prefer to start every fight against a dragon (or other high SR creature) with a Mord's scroll and forget the spell pen feats. Others get some enjoyment from being able to hit those creatures under their spells' own power.
Maximized spells will tend to do more damage on average than empowered spells. Empowered spells can do more damage, but rarely do. In the case of spells with lots of damage dice (like Isaac's), the odds of an empowered spell doing more damage than the maximized version are very small (about 0.02% for IGMS at level 17, the first level when you would have a level 9 slot to use for a maximized IGMS). As you note, both maximize and empower allow you flexibility in where you slot your spells. That is also a reason some players take the still and silent spell feats (so that damage spells can also be put in slots one higher than their base spell level).
The skill focus in concentration is not a favored feat, but it is better than combat casting, which is a very low-value feat. I wouldn't take the skill focus feat (there are items that boost concentration and the better strategy for most mages is to avoid getting hit).
Anyway, if I were you, I would probably be leaning toward spell focus evocation or necromancy for a level 9 feat (if you decide to do both, then I prefer evocation first because you won't have any nice death spells until later, but you will have decent damage spells earlier on).
You can't directly replace a previously chosen feat from the console. But, you can use console commands (specifically dm_giveXP) to remove enough XP (see the level progression article to help figure out how much) to drop below the level where you chose a feat you regret and then give the same XP back so that you can relevel yourself back to where you left off, choosing the feats you want this time through. (That doesn't work for feats chosen at level 1.)
I hope this helps.
