Op, it's better to focus on ranking, making constructive and informative posts will make it easy for you to get merit. Aren't you soon reaching 100? it will increase your reward potential more. While waiting for that, it is better for you to join the bounty campaign according to your ability, at this time, to get a lot of rewards, at least join two or three campaigns, for example article, social media, and signature. But it all depends on the ability of each.
One can focus on ranking up while joining in a bounty campaign at the same time.
Social media task isn't that hard, especially the twitter bounty where you just have to tweet or retweet in a number of times per requirement.
Of course getting your account to rank up is good, it would give you a chance to earn a decent reward in signature campaign, but the activity is also important aside from getting merit, and there's no easy way of getting it as we can see, a lot of members who got high activity but they failed to rank up as they are not getting good number of merits.