I doubt that you really need geo as an undead (cuz I've never used it in non-magic party, and everything was fine). I prefer the lifesteal from Vampiric (sco+hydro or plain mosquito swarm) and necromantic buffs like bone armor.
also I always tried to develop a habit of treating characters that lost all their armor\m.res as "already dead", because often they are perma-CC'ed after this point.
as for the build.. you have a ranger, 2h and support-summoner. i'd say you can go with a physical mage that can deal damage, buff allies with enrage\living on the edge\deathwith and etc or serve as an off-tank(necromancer, preferably with a shield for survivability and a bit of warfare skills) or a rogue type character that can use it's mobility to assassinate squishy targets in a turn (scoundrel+warfare or dual wield with a bit of poly and air)