I agree that starting in 5 gallon containers is [usually] a horrible idea. I personally wouldn't even think about using anything over a liter to start seeds, those 9oz solo cups are perfect for the purpose. Watering properly, etc. is going to be bitch in something that big. Not saying 'it can't be done', but I see folks having issues with their seedlings all the time on here and many of them are trying to start in pots that to me are way too big. With a more appropriately sized container you can water until you get run-off, and you'll know you can most likely water again in 2-3 days at least. With a 3 or 5 gallon pot it is going to soak up a shit load of water, and with no roots there to use it it is going to stay quite wet even when the soil surface dries out... sounds like a hassle to me.
Not to mention that unless you have feminized seeds that is a hell of a lot of potentially wasted soil. Even then, shit can still go wrong. Starting in a 4-5 inch deep container is just a good idea for so many reasons. Transplanting is not that big a deal. A healthy plant should have no issues whatsoever going into a larger container.