does size matter - how many genes in 1 vector (Feb/02/2007 )
the 2A peptide is not very large. I add it to my gene fragment by PCR. Ie the primer itself contains the sequence for the self cleaving peptide. There is no need to add the peptide by linker.
As for trick and tips, I am not aware of any. The peptide is very robust and works in many species (fish, yeast, hamster, mouse and human cell). However I believe you should check for protein function just in case it is disturbed by the presence of the self cleaving peptide. I believe the paper describing the 2A self cleaving peptide had joined 5 proteins, that later cleaved into functional protien. So 3 if not the limit.
I am currently not aware of any commercially available vector containing the 2A peptide. However, it is rather simple to clone in a self cleaving peptide by primers.