Surely, you can haul a mini in a minivan or SUV- once and as an emergency!
I would not dream about doing so on regular basis.
There are miniature horse trailers around already. Small and much lighter than even one horse trailer. I saw one recently at our trailer guy. It was converted smaller utility trailer. Some horse trailer places might be able to convert for you.
I think, you look into this mini party business from a position of someone, who is not very familiar with minis.
First and foremost, you have to find the right mini. Contrary to the popular belief, many are not child friendly, do not appreciate cuddling, and will not enjoy their party job at all.
It takes a special one to succeed and not just go through the moves or, even worse, start some mini revolution in the middle of the party. They have an instinctive knowledge, how to time their coup-d’état- it’s deeply in their DNA cemented by centuries of evolution!
FatCatFarm, thank you for sharing an example of such business. I thought it was funny, when you look through pictures, at every possible occasion, the little professional party mini seeks to do what the minis do the best- eat! :lol: