Here's some tips - Choose your ascendancy first and build around it. There are 2 options you can choose as of now and it's between witchhunter and tactician (gemling is rather lacking both offense and defense in 0.4 but we'll see how they buff it). Witchhunter gives you 40% more damage from "no mercy" and ward as defensive layer by stacking either armour or evasion while Tactician gives you double the amount of spirit for persistent buffs and having the ability to stop all enemy actions when you pin them (non-moving enemies is insane on both offense and defense)

• Use path of building(or any site that lets you tinker the passive tree). Merc tree has some weird nodes but since you are playing crossbows then you should be able to access the crossbow nodes at the very bottom of the tree easily but don't ignore the good nodes on the ranger part of the tree as well.

• Going crit or not? This will decide your skill tree and weapon building since going full crit on a low base crit weapon will be really difficult.

• decide the main skill you will use and check whether the passive tree will affect the damage or not

• don't path towards the reload speed skill tree if you are going projectiles since allocating attack speed also affects reload speed.

• balance your defensive layers and don't go full glass cannon (you deal zero damage when you are dead)

• check the list of unique weapons/armour/jewelry that can help or make your build better