Most points I probably would have stated Ram covered, all I will add is don't mix the two. If you plan on grinding mtt's don't mix cash tables as well IMO unless you are playing only a single mtt or something, if looking to have more tables running but not mtt's then go sng's or stt's so that you are focused at least on the same/similar format game.
Cash is different than the mtt/sng/stt format and as a general guideline it wouldn't be wise to mix the two unless you play simply for entertainment, to keep focused optimally its best not to put the strain on the brain of playing two totally diff format games at the same time. Obv just a guidline as I have often mixed them myself, or worse yet been playing nlhe tournies, horse tournies, and badugi tournies all at the same time (that will F with the brain lol, but mostly in this situation its the pstars round 1 freerolls
From an aspect of learning the game I think its best to find the format that you feel you play best in and study it to improve and beat the game to build on a bankroll and provide something that you could revert to in rebuilding if you decided you wanted to moved say from tournies to cash, at least if you take a hit in cash you can rebuild in tournies and try again or vice versa depending on which you choose. Sometimes you have to wander around aimlessly almost without focus to find where you want to end up spending your time grinding, this is where I have been for a few months. GL.