Good gloves can be a deal breaker for me for sure. I like Bontrager or Craft brands. They can cost a little up front but the Bontrager's especially take care of you if there is a problem down the way. If you dont have any other options at the time, I like to bring a pair of rubber gloves(doctor type) for mech repairs and what not. If you put them over your standard padded gloves it makes them insulated as long as you don't sweat too strongly.
As far as your soreness goes, fitting is the important starting point, but gravel rail trails are a unique thing in strength training. Road riding gives you hills and downs but rail trails by thier nature are consistent by design and gravel adds drag. That is one of the endearing features in my opinion. The drawback is you have to get used to it and when planning I try to put the uphill leg at the beginning because you will be spent at the end. Your cruise speed is very important to monitor on the uphill leg too since it will seem like you want to go harder. Just takes practice to know how hard to go.