I've had an 8-man and large stove for many years. They are well worth the money. I don't know about the competitors but my Kifaru is tried and proven. It has taken enormous abuse and few problems.
The tipis are categorized by their capacity to barely get that many people in sleeping positions; they are not intended to be used by that same number of people. Figure half the number of people, max, for each given capacity rating.
If it will always be you and your son, or less, then the 6-man should work. But you will probably end up taking others out in it and will want more room. The 8 man has been proven to be the most versatile. Not too big that one or two people cannot backpack it and lots of room for two guys and gear plus a dog, or whatever. It will handle 4 people and gear plus a pile of firewood inside but it will be a little snug.
Mice and bugs will come into the floorless shelter so choose your site accordingly. I tend to use my tipi in fall/winter/spring, with the stove, so bugs and mice are rarely a problem.
Hang all your food in a tree.
The tipi is hugely versatile. It can be backpacked with or without the stove. Its a great wind shelter. Its the best rain shelter. It can be used as a powwow shelter then campers can turn in to their own tents for sleeping.
I use mine when car camp hunting. I throw all my camping junk inside before I head off on the hunt. If a storm hits the camp I know my stuff is ok.
The stove and tipi will fit in a big gym bag. You can take it wherever you go and use it as an emergency shelter.
Most other guys in the campground have campers that cost thousands of dollars. They are a little more comfortable than I am in my tipi. When it is warm no one is in their shelters anyway.
But I am nearly as comfortable with some huge advantages. The tipi and stove is well less than half the price of most campers. I have no trailer to tow, store, or clean. And I have the versatility mentioned above.