Priming sugar in a mini keg

Hello all. I have a mini keg, 2.5 or 3 gallon one. I have been bottling all along and am very comfortable doing that. Since I want to start with this mini keg I have a thought and would like some opinions. I know what force carbing is and would like to try it but my thought is if I make a 5 gallon batch I think it would be very difficult to split the carb methods. Force carb would obviously be the easy method but I would still have 2 - 2.5 gallons left to bottle. Now I know I could make an educated guess on the priming sugar needed but I would rather not for my first time kegging. So here is my thought. Let me know if this will work and how I should do it properly. I would like to use priming sugar on all 5 gallons as I normally do. I would then transfer what I can into the mini keg and let it naturally carb for a week or two. And then obviously bottle what's left. Easy right? If you think this would work I obviously still have to use the C02 to pour. Should I just let the beer carb until ready to serve, then hook up the C02 and set it to a pouring pressure, 10PSI as an example, and pour and then disconnect when done for that time until I am ready again? Would this work?

I know a lot of you will try and get me to do other methods but for this time I am simply trying to keep things simple until I can figure out how to properly get the keg to pour correctly. So if you don't mind please stay on topic unless you have another really easy method. But I do appreciate everyones thoughts and opinions ahead of time. I know this probably isn't the "proper" method but I am simply experimenting right now. Let me know your thoughts.