It depends on the efficiency of transformation; but with an effiiency that reaches up to 10 exp3/ng with simple CaCl2-treated competent E. coli cells, and 100-1000 times more with commercial competent cells, you should get plenty of transformants if the vector and the insert have been properly prepared.
That should not be much of a problem, your I:V ratio should be maintained. Initially try 3:1 and 1:1. Basically, 50ng is used, but I got results with 20ng as well.
In theory it should work even though the ammounts are rather low. try by adjusting the ratios. there is a formula that can be useful:
Insert amount (ng) = [Vector amount (ng)/Vector size (Bp)] * Sizw insert (Bp) * ratio.
A good ratio is 3, be aware that the limiting factor here should be the vector not the insert.
In my case I was always adding 100ng of vector (so if my DNA concentration was 20ng/ul then I added 5 ul in order to have the 100ng)