You mentioned building a tiny home. Are you parking it on your land? If not planning to travel all over the US, its a good buy, for you. $3,500 is a low price for a clean chassis. Low cost up front is easier to recoup some losses later. But only if you are not adding milage & maintenance costs.
As a full time, traveling residence, it's not a secure living quarters due to the risk of being stranded while it's being repaired.
Check the hours. Looks like an activity bus from Stockton/Modesto. Maybe 10-12k hours, only. Then scoop it. Hours tell you as much as miles, can even contradict our first instincts.
"A man is worked upon by what he works on. He may carve out his circumstances, but his circumstances will carve him out as well."