Which glue/grab adhesive type to use with OSB 3 boards and joists for shed + spacing
Adhesive is used for sub-floors in homes to help eliminate squeaking from flex/movement. 

Since this is a garden shed i do not know that is necessary. Just use lots of deck screws. If you want to there are several that would be sufficient. Here is link to a page that tested several, You can choose.  

I think using 2x4 as floor joists is not a good idea,  I do  not know what size your shed is or how much storage weight it will hold so i cannot advise on joist size.