Hello again, here comes a bunch of questions :)
1. Is fullplate much better than fieldplate speaking of bashing? What about PK?
2. What is philosopher's stone in alchemy? Can't find its description.
3. How much is the crown of magi spell cost reduction?
4. Is dexterity of any importance here besides avoiding hits from players?
5. If you're an Ur'Guard interested in both pvp and pvm, what would you choose: orlach, igasho, krokani, viscanti or human?
6. Will level 80 mugwump geomancer be good in PK without arties?

1) Not certain. I believe it's a pretty noticeable difference in both.
2) Boosts the amount you sip health/mana/bromide for.
3) One third reduction on the mana cost of magic spells.
4) In Lusternia, dexterity affects what wound affliction warriors will give. Higher dexterity will give the stronger wound afflictions more easily.
5) Igasho/Viscanti
6) Very.

6. Depends.

I roast geomancers frequently with just straight damage. Very very very few (even at level 80) can keep up with low constitution because the class gets no magic resistance.

5 and 6... RP.

Creative people can effectively roleplay any race

3. Wasn't that reduced to 1/4?

No. It is 33% to my knowledge. It doesn't really matter though except for Celestines. Aquamancers/Geomancers don't have anything (to my knowledge) except for maybe Illusionary Wounds that costs a lot of mana.

The only reason it benefits Celestines is because Heretic, Infidel, and Inquisition are very mana costly... and trueheal technically costs 1000 mana (you cannot trueheal if you have less than 1000 mana, I killed Amaru in the arena this way)... but that would be reduced to ~670 with crown.

When i was using Magi Crown it only reduced mana cost by 1/4 not 1/3.

My magi crown, too, only cuts mana costs by 1/4.

Meh, if I could be a level 80 Mugwump with a few trans skills, I'd go Hex Nihilist

Geomancers with Psionics get magic resistance