1) Tempus Fugit gives you and your group +10 to speed, and gives all opponents -10 to speed. In theory, this means you and your party get around two more attacks per round, while they get two fewer.
Congeal Time halves the speed of any opponents who fail their Willpower saving throw. The only ones who ever fail their saving throw, however, are low level creatures you'd have no trouble defeating anyway. Based on prior play, it appears to affect every creature within range, but only the first time they come within range — kind of like the D&D "Cause Fear" spell.
2) Your heal/fatigue recovery rate is based on your Constitution. It maxes at 6 per ten seconds (real time) at 17 CN; if your maintained spells drain you faster than that, the only way to recover without quaffing potions is to cancel one or more spells, and just wait. If you're not inside a dungeon, then you have the additional option of sleeping for a minimum of one hour, which resets your Fatigue bar as well, but also cancels all maintained spells.
Later on you'll have the option to master one college of magic. Spells from a mastered college halve their casting cost, but have NO effect on maintenance costs. Still, casting Harm at two points instead of five is a big plus.
3) No. You are the Chosen One. Somehow, everyone — from ailing wolves to the Molochean Hand — knows this.
Which is why, at the start of every battle, your followers tend to run out ahead of you: opponents are rushing you, but will stop and fight anyone else they happen to encounter first.
4) Except for firearms and detecting/disarming traps,* Perception is a dump stat. It extends the range you can scroll offscreen (your PC can see further) and supposedly increases long-range accuracy. But let's face it: even if you depend on bows or thrown weapons, most battles happen at a close enough range (sometimes even Melee range) that those small bonuses don't matter.
The strength of spells like Harm is directly tied to your MA: max it out by learning 20 spells (17 if you're an elf, or 19 if you have elven heritage) or boost it by wearing a Dark Helm (which negatively affects alignment: it's basically a portable Sold Your Soul background). Teleportation is a good spell to invest in, since walking everywhere gets tedious.
Throwing is also a good choice, since it doesn't depend on Strength; but it does depend on Dexterity, both to increase your action points (i.e. number of attacks per round) and to allow you to invest more points to increase your accuracy. Gypsies sell a good throwing weapon; and the throwing master's quest weapon is the best one in the game. (Protip: complete the quest by giving it to her, then burn a Fate point to pickpocket it back. If you attack her, the whole town rises against you.)
*And even here, you can work around a lack of PE with magic: the Divination spell Sense Hidden. There are only three or four locations in the game where traps are common enough to be a problem, and only one of those actually occurs along the main quest.