The custom suits should cover everyone's ass. In shorties or semibaixinhos, it stops right in the curve of the buttocks to the leg. In others, it may go down one more tico if necessary, always thinking about equalize leg and trunk (pants and jacket) to visually divide your body into equal sizes.
And always bet on ever single breasted jacket double, as this is a tricky kind in many ways. Indeed, one single breasted 2 button is the most democratic (and trumps pros shorties). One of 2 and 3 are considered classic options for those who want to know.
As for the pants ... they do not need a belt or suspenders to stay in place no. Have to stay in them without any help. Pants that need a help to stay in place is not for you. And it is to stay tight at the waist so little. It can and should be comfortable yes, but nothing like exaggerations requiring extra help. Just enough to fall well not retain movements and put his hand in his pockets with some grace and comfort.