i am aware that i need 100 str in order to wear a concerto, so my question is, what level should my overall be? i see lvl 90 equipment that have 10str, but that requires 90dex should I just settle for an overall between 40-60 that has atleast 10str? also, what should be base str be?
As long as you get the full effects of the stats on your overall, it doesn't matter what level it is. For example, if you had a level 90 overall with 10 str and 20 dex, it'd be the same as a level 80 overall with 20 str and 10 dex. If you had a level 90 overall with 11 str and 19 dex, you'd pass the requirement for strength though so it'd be pointless. Higher level overalls can have higher base stats though so keep that in mind. I don't understand why you're asking to settle for an overall between 40-60 with at least 10 strength though. As for your base strength, it should be exactly what your equipment allows for, whether that be 4+96 or 60+40. As you improve your equips, you can lower it as needed.
Just get a pirate overall that has dual stats and scroll a godly clean one. Base stats should matter all that much as long as you start scrolling a ~12+ clean overall. As for what level it should be, the lower the better. The level 60 overall would be ideal because it's the lowest level pirate overall that gives dual stats and you could wear it without adding any base Str.