I'd keep the tubes in the tires. Been down that road. They probably came tubeless, and the owner saw that light. For what it's worth, the skid steer is about the only machine other than tractors that I run tubes in. What I've found is that with such narrow tires relative to rim width, if I hit a curb, or even get down in a frozen rut, that's enough to either break the bead or bend the rim and let the air go... in one big whoosh. Tubes are a pain at times, but not near the pain of having to go to town to have a tire blown back on the rim with a bead blaster.
Tires for those things tend to be fairly standard sizes, and the size ranges are wide enough that you aren't jumping to the next largest without changing a wheel. I run 10.00x16.5's on a (I think) 9" rim. Wish I had more.... Frame clearance is generally the issue with running larger skins.
Not sure about oil changes on that model. On my NH, there's no drain. I just slap a hose whip on one of the boom connections and blow it out in a bucket, then shut her down quick when it stops. Change the filter, and fill with new oil. I tell ya, they though ahead on that design.... no fricken drain plug. Good luck.