Welcome back too! Been wondering what your shopping is up to.
The used
L3130 is a very reasonable choice, but the price sounds a little high. There may be new ones left over that you could pick up for $18k or less, brand new with warranty, same loader, tires, etc. If you can get it to $15k or less it starts sounding like a deal. As of a month or two ago Williams Farm Equipment in Charlotte had a number of Lxx30's on the lot waiting to be sold, including one or two
L3130's. They've been stickered at something like $18,900 since last winter, and I have to think that if they're still on the lot they would be VERY interested in selling them. Williams is a pretty big operation and I would imagine they could deliver up to you. I didn't buy my tractor there but I did shop them and I have bought an implement there - they've been quite good to deal with.
The HST on the Lxx40 series is improved, but the HST on the Lxx30 series works just fine. The most significant difference, IMHO, is the pedal design. There are a number of technical "upgrades" on the 40's but, again IMHO, they are neato features rather than really necessary or useful.
Of course I like warranties and new stuff and it's easy to spend other people's money.
Michigan tax law is pretty clear - ag, forestry and plant nursery use is exempt from sales tax, anything else is taxable. My understanding is that you are actively breeding horses for profit. That is an agricultural use and you should be able to legitimately claim the sales tax exemption. Of course this advice is worth what you paid for it. Do note that there is no tax exemption for used equipment, so whether you pay sales tax or not depends on your ag exemption, if it's appropriate, and not which tractor you buy.