What is more important...anatomy or tactics? What is the advantage of each of them and whats the advantage of having them together?

Give the rest of the template, suit and tactics planned. Taken out of context like that, a proper answer can not be provided.

In general, since we're unsure what you're aiming for as of yet, Anat's biggest benefit is max healing and better chance to rez. Tactics is strictly for damage increase.. if you have a good DI on your weapons and/or jewels, dump anat as the extra 9 or so points per hit is not worth the 100+ points which can be better used elsewhere.

unless you have healing there is really no reason to have anatomy.
Used to be the anat+eval=gm wrestling for defensive purposes, but now with the mage weapon items that isnt even really a factor...dont know of any mages that would waste the skillpoints into anat anymoer for that reason when they could go inscript or ninjitsu (or tactics)
Tank Mage w/ decent tactics is pretty nasty land a 40 damage armour ignore with an explosion precasted....

anat gives like damage increase 65 at gm

You sure? I know it used to pre-AOS.. but I understood that it had been changed and in no way effects combat any longer. In fact, on the damage calculator on Stratics there is no field for entering your Anat to calculate chance to hit/damage either.

combat calculators
oops - damage increase 55 for gm anat, 65 for legend

anat still does add damage... In fact, many chars now have no tactics at all and achieve damage cap from anat and DI from items / weapons. WIth Bushi, Specials and honor...even GM anat is lethal if your char is set up right.

I see... hmmmm... meh.. I'm gonna have to stick tactics on a soulstone and see how I do without it.

Thats a good call. Just try to stack Damage inc on your jewels and weapons and other items and you should be fine. If you can get your bushido up, use Lightning strike with a good mana leeching weapon and you are golden. Chiv for devine fury, and have at least 140 dex for quick bandages.

UO in easy mode.