I am installing 1/2 engineered Brazilian cherry flooring that is 3-1/2" wide. I have OSB subflooring (not sure how to tell if it is T&G since it is installed) that is nailed down 15" OC. Will running my flooring parallel to the floor joists have issues like sagging and gapping problems? I will be face nailing and gluing the first 2 rows then blind stapling the rest of the rows over felt paper. The reason I ask is if I lay the flooring perpendicular to the joists it will be going the short direction of the room and look strange, but I can live with that if the alternative of installing it parallel will present issues.

Thank you,
William Morris

Engineered floors follow the same guidelines as solids..... should be installed perpendicular and the OSB should be 3/4" thick, not 5/8". No one can say if the floor will ripple or not..... it's your house so take that risk into account.

Definitely do NOT install parallel to the joists if that is also parallel to the natural light source. Any irregularities will be visually enhanced.
If you add a 3/8th or 1/2 inch PLYWOOD underlay after sanding the OSB flat and true, you will then have a sub-floor system that will accomodate a parallel installation.