Probably your best bet at getting the information, or at least a viable reference, would be to enter
<90th. Infantry Division WW II> and SEARCH,
which will bring up a contact related to the 90th.ID Association.
His name is : Alan G. Connett P.O.Box #730 SouthHill, VA 23970
He lists an 800 number, 416-9090.
I think it indicated that Alan is the primary contact for the association.
As for your chance at attaining battalion/company/squad records, I think the answer is NIL. Most of those records were lost in a major fire at the Military Records strage facility in St. Louis, MO back in 1973, so, there's nothing there.
Hope Mr. Connett can provide you with some individual personnel material, like diaries etc..