New compost set up questions

I have been researching all about composting and I think I want the 3 bin system. I have read about what to put in and what not to put in. I would like to have a holding bin for leaves and another one for grass trimmings. Since I don't have any leaves yet to make the pile with, can I put the grass trimmings in a holding bin? If so, how should I go about it? I know I just can't throw all my trimmings in there or it will get slimey or something. Do I have to dry it out first before putting in the holding bin? When I mow grass I have about 4 catcher bags full. Any help would be appreciated.

There are other things you can use besides just leaves for the 'browns'. Shredded paper works admirably. I think if you just put the grass trimmings in a bin by themselves they will get stinky and slimy quickly. Note that dried out grass trimmings is then considered a 'brown'. You don't have to be really precise on it at all.. Put in your four bags of grass clippings then cover with paper shreds or just hand tear up newspaper to cover.