Hi and welcome back in ReQQ !
first : i reply to this topic in order , i hope, to help you a bit but i am more specialist about fighting sins than playing it
there are links for a skill calculator in theses forums, but as i am quite a noob at using it in an optimal way , i can't assure you where to find it even with the search options. hope some will be more helping about that.
about the build , as you may remember sins are the " heavy dps one by one" type ( AA- Auto Attack)...unless you play more SS ( Skill Spamming) what is said "noobish" by many. ( mixed is near being considered the same way. )
most of the sins IG play AA , and use slow skill second job (sorry don't have the name in mind right here), stealing weapon, soccer kick , brutal scud , home trust, dash skill and retreat skill , stealth of course. buffs are the quick attack and the deadly cry added to fortitude. i would say max all theses skills for AA and you will still have some points to dispatch i think but as i said , i am not a real sin player even if i tried it a bit and fought it a lot
for the gear , trinity weapons (duals sword and Xbow) have OP damages, and the set nightmare 89 for sin can be very OP i think (dropped on a boss called Mare-Gall).
i would have a lot more to say , even as a non specialist and i use a lot of shortcuts here . in fact , what i even start to write was turning to be very "bigger" , but :
-i had a big day work ,
-you would end tired and bored to read all i would have to write
- some specialist would give after more specific infos on the numbers of DNA/skills points where and why...same with gear, making my post a redundant ,less helping one.
hope to have help you at last even a bit ( at not feeling alone at last )
don't hesitate to join some active guild and ask assistance and answers in game too. and sorry for my fluctuant english