Surely the best way to play him early is using sharpshooter and taking archery for the plus 2 to offset the -5 penalty? Dread ambusher will give you advantage against creatures with darkvision. Hunter's mark for extra damage. Sneak attack on the attack that hits. Get to 5 with gloomstalker either after rogue 1 or 2 (cunning action is a lot more useful now only rogues can hide as bonus action, will offset the -5 lots, plus you want hunter's mark too)
Then it's just a playstyle choice of whether you want the alpha strike of action surge first or the extra bonus action of thief, which would be really useful for a ranger rogue for the options.
Then dual wielding for hand crossbows and crossbow expert for the late game and Astarions first round is 3 attacks main hand, one with sneak one with 1d8 dread ambusher, two offhand all with dex modifier then action surge the whole lot again, with each of these having a +10 to damage *each time*. Boss killer first round. No room for an ASI so hags hair at least needed to get dex to 18
