Hi MS, Firstly welcome to the best place for your inquisitive mind on the net!
Secondly... I am not the guy who is going to be able to answer your question well.... As I'm too scared to attempt a stirling just yet! :-\
I have taken to a Safe road of discovery, I built a treadle/finger engine first and then progressed to a little steamer, I now intend to build another slightly more complex steamer and carry on increasing my skill as well as my engine collection!
I think of Stirling's as requiring a great deal of accuracy.... This I do not yet have, so I am making the steamers etc to help me get to the point that I am confident enough with my machines and my skill level to tackle them.
Many others have built stirlings as a first/second engine... Hats off to them cause I am still of the opinion that I need to practice more!
Ask Twinsquirrel about his first stirling (engine of the month) he can give you some first engine advice I bet?
Then there are the old sage like super knowledgeable builders... they know who they are! soon they will write something for you I am sure ;D
I know... I talk a lot for someone with nothing to say. ;D So I'll leave you with this..... Keep building, sooner rather than later you will end up with one you can't stop smiling about
Ralph.