Any tips on how to spend Ability Points?
Just experiment with different skills and see what you like, the game is not that hard even in Death March difficulty. Re-spec later is easy anyway just buy Potion of Clearance.
If you want an easy time, I recommend invest points in light attack tree, max out whirl, max out razor focus, battle frenzy, cat school tech, then use Cat school gears. Then Whirl to win with all the crits and never run out of adrenaline. Throw in igni for crowd control (due to burning) and Alt-Quen for healing in battle.
Also level 3 Axii for dialog choice and easy battle in early stage of the game.
Oh one other thing, the crossbow is not for damage. It's for debuff. Alway craft some bolt that does 100% bleeding chance and keep them in hand, It's almost cheating against many boss because Bleeding from bolt scales with enemy hp and last for a long time.