@justnumbers
There is no flat earth model, not in a scientific sense of the word. There are many potential and proposed ideas for a model, but that is it. I highly recommend the wiki here for a general overview of some of the ideas/concepts around.
Models are a big part of what got us into this mess, and they will not be helping us to dig our way out. Most flat earth researchers devote their time to more meaningful/useful endaevours than playing with models.
That said, your list of questions is good and you should attempt to answer them for the presumptive model you are playing apologist for! If done earnestly, it should be enlightening.
Here are the honest answers below, though they have nothing to do with the shape of the earth and are correct regardless of the conceptions thereof.
1. What is the diameter of the Earth?
No one has any idea. For the earth to have a diameter at all, it must be circular in some fashion. The basic shape of the world is not known, or measured. Many people have CALCULATED this believed "diameter" but no one has ever measured or confirmed it in any way.
2. What height above the Earth is the Sun at?
No one has any idea. You would ALSO need to measure this, but no method has been devised to do so (though there are some that BELIEVE they can through mere calculation with no validation). Parallax does not work for the lights in the sky (and most all distant objects).
3. At what radius dose the Sun rotate around? (I.e. how far is the Sun rotational path from the center of the earth?)
It is suspected that it moves in an oscillating but mostly circular (possibly many ellipses, like a spiro-graph) path that is roughly the size of the equator. It varies in height/distance as well as radius over the year, but the average/center/median would seem to be, essentially, the equator. The distance from the center of the earth (if such a thing exists - humanity has no idea) to the center of the sun (if such a thing exists) is completely unknown and a wildly fanciful question. It has the same answer as 2.
3. What’s the diameter of the Sun?
No one has any idea. We (humanity) don't know the composition, mechanism, distance, size, exact shape, or nature of the sun. We teach children we do, but we lie to those poor children - early and often.
4. What height above the Earth is the Moon at?
Also unknown, it would have to be measured first. Contrary to popular opinion, and massive television advertising to the contrary, nothing like that has ever happened in reality.
5. At what radius dose the Moon rotate around?
It is also thought to be similar to the suns's, albeit with a slightly different speed around the track.
6. What’s the diameter of the Moon?
See question 3 and replace "sun" with "moon". The lights in the sky are a complete mystery to us, and rather than convey that honestly to ourselves and children - we decided to lie about it rather than appear uninformed and ignorant. "We don't know" is the honest answer to most questions, and you rarely hear it in the classroom. "Best guess" religious mythology is inserted in its place and disingenuously and erroneously presented as "science fact".
Flat earth research is largely about identifying, critically evaluating, and ultimately excising belief from knowledge. Belief has no place in knowledge/fact, least of all scientific. Much of what we were taught, especially as small children, was untrue and much more was religious/philosophical dogma being passed off under the guise of science to children. This subject is about the following 3 questions, in my view :
1. What do you know (with certainty)?
2. How do you know what you know (and how do you derive that certainty)?
3. How do you share what you know (and that certainty) with others?
If you critically evaluate the questions you BELIEVE you know the answers to (because of conditioning through rote under the guise of education from childhood), you will find that you do not "know" these things with any certainty - and no one in the world does, they merely parrot them as they are required to, to matriculate.