it may be counter-intuitive, you will often get higher transformation efficiencies with less DNA, especially when using highly competent cells. If you used 100-1000ng of total DNA in a ligation you will often get more colonies if you use 1ul of a 1:5 or 1:10 dilution rather than 1ul directly.

http://www.addgene.org/plasmid-protocols/bacterial-transformation/

Yes. When you use less amount of DNA and more cells,probability of DNA getting transformed increases. 

Yes, higher amount of DNA reduces the chance of transformation. It may happen due to competitive inhibitory effects of DNA. Not only that, in case of ligation,mixture not only contains DNA, but also contain other substances,enzymes,buffers, co factors needed for ligation, that might hinder the whole transformation process when higher amount of ligation mixture is taken.