- The stuff you can buy is just cosmetics really. Loot boxes will have some armor you can infuse up if you want (it starts at 3 light) or some chroma which applies different colored lights on certain armor (armor from loot boxes and faction packages). There are also some other packages that you can buy from earlier, personally I'd go for the SRL package. You can get a cool looking Sparrow as well as some funny horns to use while riding around.
- You can actually get to max light by doing basically anything. You'll get good light gear by doing the weekly endgame stuff, but for the most part crucible and vanguard strikes work well. Packages from factions/vanguard/crucible can drop up to 6 light above your current overall light, so farming them works pretty well too.
- For weekly stuff, you can do the nightfall, but it's not always worth it (especially once you hit light level 330). Challenge of Elders is pretty good, since you get one weapon and one piece of armor per week from Variks, as well as a chance at secondary weapons and ghosts from the Challenge itself. The raid is probably the best boost you'll get, since gear can drop up to 6 light above your current overall (that's the general rule of thumb for legendary drops).
-Sparrow Racing League was a limited time thing in December, and a lot of people want it to come back. It was cool and had some exclusive armor/shaders/etc. that a few people are annoyed that they can't get anymore.