No, it doesn't negate MR- but as a sampire, you really don't need mana regen.
As for lightning strike- I only use it if I don't have mana to armor ignore. That is why Mana Increase and Lower Mana Cost are so important. There are exceptions (like Rikktor) but I pretty much just Armor Ignore every swing in every battle. Well, that or Whirl Wind. Mana is only a problem if I get Mana Vampired or get some unlucky rolls (the amount of mana leached is random). I want my mana at least equal to the amount I need to AI twice at double the cost. So, that is like 48 mana. Really, if you haven't played one before, playing a sampire is really different than playing any other template (or at least the way I do it!).
As for crafting, I am sure there are others that are better than I, but this is how I do it.
You know that you are going to be imbuing Fire on each piece. So, when crafting the pieces, you want fire as low as possible. For plate- I look for pieces that have a base 5 or less in fire. Also, Physical. Because plate pieces start with 5 in physical resist- using mace and shields (25 physical resist) and enhancing you really need as few points as possible in physical as well. I look for pieces that have 11 points total or less between the 2. That means that only 3 points (or less) of the Arms Lore/Exceptional bonus are essentially wasted. I literally craft hundreds if not thousands of pieces for each suit I make.
Then, as I make each piece, it really doesn't matter what slot you start with, but I make pieces until I get like 5-10 pieces per slot that I am happy with. Then using a spread sheet, I start mixing and matching the pieces to find the best fit.
This is the order of how I do it-
1. Craft the pieces
2. find pieces for the suit
3. PoF the pieces chosen for the suit
4. Imbue the suit
5. Enhance