my Keezer project

I'm going to start making a keezer with a coffin box on it with 5 taps in all. I have a few questions. I know i see lots that say not to mix kegs but i was thinking buying 4 more pin lock kegs alot cheaper. it is just the fittings for the pin lock over the ball locks that are different right. so as long as i have 1 ball lock connector and 4 pin lock connectors i will be OK. also Do i need the multiable regulators for the system or can i just use one pressure on all the kegs after they are fully carbonated. thanks for any help you can give

There is a convenience of being able to interchange all your disconnects on all your kegs, but thats all it is. It isn't a necessity as long as you have enough connectors for the kegs you have. The different shapes between ball lock and pin lock could affect configuration, but that is mostly dependant on the shape and size of your keezer. If they fit, you're good to go.

As for the regulators, no you don't. You can easily set it up with either a distributor bar with shut off valves or just a bunch of T connectors. I would caution you against the T without valves method, as it can be a real pain to find and fix leaks when you are unable to isolate sections of air line, but if you're really on a tight budget it can be done. Also, valves and multi-body regulators are easy upgrades later on if you decide you want to expand the flexibility of your system. There is a benefit to having precise control over each keg's pressure individually, but you can still serve good beer without it.

I do just like Blue says. I have one keg with the pin lock and a 1/6th keg in addition to four ball locks. I wanted to be able to use whatever keg I happened to have filled at the time so I use disconnects that are threaded so I can take one off and put another on when required. I also use one regulator and a four outlet manifold with shutoff valves on it. Works just fine.
I find it a little bit of a pain to change the disconnects but really it only takes a couple minutes and it's not that big of a deal.
+1 on the upgrade latter if you find you have a need for it. I haven't seen a reason to do that yet but maybe someday I will.