D&D 5E What to do at lv 4

So im starting a new session with a new dm. He told us to make lv 3 character with point buy.
So my character :
Race : Stout Halfling
Background : Outlander
Lv 3 Ranger
Archetype : beast master
Skills : athletics, stealth, animal handling, perception, survival.
Str - 12
Dex - 16
Con -14
Int - 10
Wis - 14
Cha - 10
Beast : Giant Wolf Spider (imma spider rider!)
Didn't take the giant poison snake cause didn't want to have stronger monsters .-.

So question, do i up Dex or take crossbow mastery at lv 4?
I plan to eventually switch to a hand crossbow and take the feat anyways but which should i take first?

If you want damage, then crossbow expertise.

If you want defense and skills, dex.

As a beastmaster ranger that will habe other things to do with its bonus action, I would hesitate to limit me to crossbow mastery. Dexterity should be your best choice. If by level 8 you find yourself not using your bonus action or you find yourself in melee more than you wish, you may reconsider.

Between the two options you mention? I'd pick Dex. More AC, more initiative, another + to hit & damage with ranged or finesse weapons.

Since Wis is your casting stat, are you happy with your spell DCs etc? Your bonuses on Wis related skills?

I'd generally go Dex, though part of it is if you are using the PHB Ranegr or the UA Revised Ranger.

With only a +3 mod, I'm not sure switching to a smaller damage die and getting an extra attack will improve your damage significantly more than just +1 to hit and damage that Dex will give you. And Dex will improves so many other things as well.

Hmm, let us math. I'm assuming no magic weapons.

UA REVISED RANGER

18 dex: Heavy Crossbow for d10+4. Average 9.5. "Standard" 65% chance to hit. 9.5 * .65 = 6.175 expected damage per round. (Loading gives no penalties without extra attack)

16 Dex + Crossbow Expert: Hand Crossbow for d6+3. Average 6.5. 60% chance to hit (worse because not advancing dex). Two attacks. 2 * 6.5 * .60 = 7.8 expected damage per round.

Okay, turns out I was wrong. Crossbow Expert will give you about 1.6 extra damage per round. The opportunity cost for this is your bonus action every round, -1 to AC, -1 to Init, -1 to Dex skills and -1 to Dex saves. This is a toss up if you want to do more damage or more skilled and defensive.

If your favored enemy bonus comes into play a lot (say you picked Humanoids), that would tilt me even more in the direction of the Crossbow Expert since you could apply that to both attacks.

PHB RANGER

No chance for favored enemy damage, but at 5th you'd get Extra attack. The math (@ 5th) would then be:

18 Dex: 2 attacks @ d8+4 (8.5 avg), 65% = 11.05
16 Dex + Crossbow Expert: 3 attacks @ d6+3 (6.5 avg), 60% = 11.7

Because in this the extra attack is only +50% # of attacks instead of +100%, the difference is little. I would definitely go for Dex with this set-up because of how much it brings you.

I am going to echo others. My choice, if I was playing this character, would be more Dex. Out of the two choices, Dex has more impact on the Ranger.

This is your character though, so ultimately, whatever you feel is more thematically appropriate.