Looks like I need to get some Vanguard merits. Should I bother upgrading the vendor gear or just save the mats for other armor?

I don't think you need comendations anymore. Also as you rank up the factions they will send you packages containing legendary gear or weapons. Look at the armour light level if it's 36 light it can get you to level 32 32 light=31? Anyway for the mats once you reach 26 or 27 you can start doing vog normal, on hard you start getting double rewards (also gets you way better guns than you currently have) So recaping 1 rank up faction or vanguard of choice with bounties, daily story missions, weekly heroic strikes, and if all else fails patrol and public events 2 if lacking ascendant materials get groups off the forums to go play vault of glass This will be enough to get you high leveled enough to complete the story included with how on normal difficulty. Now you need to decide what you want to do, to continue with endgame activities like raids weekly nightfall and PoE, you want to reach level 32 at least, you can do that with 36 light vendor gear or crotas end armour (you can do crotas end normal at level 30) I'd recommend the vendor gear since it requires acendant material instead of radiant materials required by crotas end (which you only get from doing crotas end) Hope this helps let me know if you have more questions!