I am playing a Sillix trader and I am at lvl 19 currently. If I read the rules correctly, when I reach lvl 20, my safety period will end. Should I avoid missions and stay under the 20 limit until my protected time is up? Or, should I forge ahead and finish missions as fast as possible.

Well it depends on whether you care or not about being disabled. As much as everyone likes to get huffy and puffy over being "killed" it really dosnt do much. As long as you can make around 130%+ of your daily upkeep from minerals you should be fine and id just focus on ranking.

If you do care then check out your battle tab and see if your up to par module wise, if you are you should be fine and should focus on ranking.

Now if you arnt well you could stay at rank 19 and research better modules, but your protection runs out after 2 weeks of playing and unless you have some very, very good planets your only going to loose research production by not ranking/ getting more planets.