The best way to use your three tat slots is these dyes:
+4 str -4 con (hit harder)
+4 dex -4 con (crit more and hit faster)
+4 wit -4 int (remote chance of resistance to Hold, and resistance to curses, and "int" stat is not used by you, so there is no consequence for a TH draining int stat)
This is standard DD melee tats. Don't waste your slots on smaller dyes, if you can afford four dyes.
Get a set of plated leather and keep it, even after you get B and A grade later. You'll use the PL set for the +4 str bonus even later on when you are assisting tanks.
All the Tatoos reduce more con then you gain in dex.
Only those you can buy in the shop.
+x/-x are drop-only and can be bought from other players (farmers) at crazy prices. Don't pay more that 100k for a +4/-4 dye.
Edit: I forgot, you can also get them from the merchant of mammon, of course.
As you're only Lvl 45, if you dont have millions of adena to burn, you could try some +4/-5 tattoos. They are good value for money (~660k per tattoo) and make your levelling a lot faster. You're a human with a lot of con, after all, so dont worry about 1 or 2 con more or less. (1 con equals about 60 HP on your lvl)
Armor is right, Plated Leather ftw, until you can afford A-grade