Weapons that were from year 1 will not upgrade to the current light level, with the exception of year 1 exotics being brought to year 2 and 3. As for leveling up, it really depends on where you are in the game and where you want to be. Also, depends if you're a solo player or you group up. I would probably just Google the best routes to take, assuming articles found there will go into greater detail.
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Thanks