Congrats - I have had 2 C-sections already and am 24 weeks pregnant with baby number 3 - which will also have to be a section.
I had always assumed that three C-sections was the 'safe limit' until I read an article in a pregnancy magazine which said there was no recommended limit. I think the only thing they make recommendations about is whether VBAC is sensible after 2 or 3 sections.
I have never, ever had any problems with my C-Sction scar either - so I reckon that should play a part too.
Good luck and enjoy it! Wow - #5. How old are your kids? So when are you going to get this recommended rest in the third trimester?