My slow build OLB is training spd/tck right now after 68 capping agility. After he finishes speed, I'll probably train str/tck, cap tackling, then train vis/cnf, and second cap vision. He will be an OLB but he could play MLB too probably. A MLB around level 40 should have strength and tackling over 61. You could probably get by with leaving speed at 61, which will be a lot easier to do than 68.
For a MLB, get strength to 61 and then decide whether to increase it based on the players in front of you. If you have a good NT who keeps two o-linemen engaged on almost every play, 61ish is probably good. If not, you may need more. You'll have to watch the replays to know for sure.