I don't know that there's really a "traditional" assassin build for Arelith, as until the
March update they were pretty bad and people would generally just take 5 levels for access to the assassin's guild.
At this point? For a dex-based assassin, I would plan to take at least 16 levels. This gets you the upgraded version of all the spell-like feats, a hefty assassinate damage bonus even with mediocre int, and access to epic dodge. Don't sweat strength too much, as low-strength characters have gotten a buff to their carry weights. Take at least 4 levels of a full-BAB class by level 20 to get a 4th attack/round, and plan to for one of your lass few levels to be a class that lets you dump points into discipline, as that is a skill that just about any build wants to max out.
If I were to tweak BT's fighter/monk/assassin build, for instance, I would probably do 8 fighter/4 monk/8 assassin pre-epic (for a BAB of 17), and end up with a 10/4/16 spread, taking one level of fighter at 24 for epic weapon spec and one at 29 for a discipline dump. End the build on a level of assassin and the epic dodge feat. I would say that melee-focused rangers on Arelith are actually better off with strength builds, even when dual-wielding, which is enabled by the
Ranger's Runic Studded Leather and its lesser variant.
Equipment-wise, most of your gear (cloak, belt, boots, gloves, amulet, rings) for the majority of your levels will be either be custom enchanted or the randomly generated magical items, which can give +1 to up to 3 stats/AC and +2 to up to... 4 skills, I wanna say? Take a look through the
crafting section of the wiki to get an idea of what gear you can expect in the end-game, especially in the tailoring, helmets, special weapons and special armor categories. You can generally expect to get +7 to two stats pretty early on, so you'll be hitting the +12 buff cap on those fairly easily.