During the Dark Ages, you should really bother with the 3 physical attributes primarily. Many decent weapons and armor. Especially the full plate and heavy melee weaponry. You should also save/load before speaking to vendors, so as their stock gets renewed. There is better quality in items, such as exquisite titled and one else category, which is slightly inferior, but i now do not remember. Holy and Unholy? Don't bother with. During your crusader era, you won't have raised a sum worthy of buying such an expensive item anyway. And while undead, it is not smart to lower humanity so much, as to wear an unholy item. Disciplines? You get large/vast amounts of xp to max them, during modern times. So it is then you should put effort in them.
For disciplines, raise their stat only to the limit of them being useable/castable. Don't bother with the appearance effecting stats, there are items that do this just fine (like the diamond set of jewelry). Be stingy with blood and ammunition, sell most of them to get gold/paper money, and buy/invest into heavy armor items and exquisite melee weapons. There is also a trick that helps your ancient helmet (try to buy/find an insulated one, it is a magic item category that adds lightning resistance, and final boss has very dangerous lightning damage) and some other certain ancient gear like weapons transfer to modern age, but i do not remember the entire list.
For getting the insulated great helm, save in Vizherad Castle entrance, before opening the big chest upstairs. Try that chest and load game until it is dropped from inside that chest.
