50% is the max mitigation you can get for any one type of damage.

Spell resist affects fire damage if it is magicka based.

Fire resist (or specific resist) affects any fire based damage (magicka based, stamina based (bow line, for instance), or environmental).

Specific resists are always more effective (2x) than generic spell resist.

The easiest way to check your resistances are with Harvon's (sp) Extended Stats. It will show you the baseline numbers for each type.

Your max amount would be three Legendary enchants on jewelry for specific resist. Even at Vamp stage 4, one is usually sufficient, so long as you have some quick footing.

One thing I forgot to add, specific resist and spell resist do stack, up to the 50% mark, so you'll get some mitigation from both, but the specific resist will always be more effective.

I normally try to have multiple versions of the jewelry I use, just so I can swap out different resist enchants as the situation calls for it.

And for those that say you can't do certain content because of (Vamp, usually), don't buy it. I've covered the gambit. You do have to be more aware though.

Makes playing a 'normal' character in such circumstances a piece of cake, too.