Older Class Cs on a Ford E450 chassis have a GVWR of 14050 pounds, while newer E450 chassis have a GVWR of 14500 pounds. I think the GVWR improvement came around 2008 model year. There is a correlation between length of the Class C to Occupant and Cargo Carrying Capacity (OCCC), i.e., the amount of weight the chassis can carry without exceeding the GVWR. A longer C generally means heavier weight, thereby reducing the OCCC. In other words, the longer the C, the less people, food, water, and stuff you can safely carry. Additionally, the more options on the C like slide outs and leveling systems further reduce the OCCC. So a big question for you to answer is, "how will you use the RV most of the time?". If only going to the camp grounds on the weekend, and you don't need to carry much stuff, a longer C with slides may work fine. If going on cross-country trips or full-timing, you might need to find a C with a larger OCCC so you have the capacity to carry everything you might need.
Is a 30 harder to drive around than a 25? I don't thinks so. But, a 30 will be harder to park around town. Further, a 30 may be harder to park in campgrounds, especially some of the national and state parks.
Can't help with the insurance question.
The risk of buying a rig 10 years or older depends a great deal on how the rig was maintained. Carefully review the service records. Some on the forum advocate buying an older rig from a rental company who generally take good care of their property. But, in any case, a good first-hand examination of a potential rig is in order. The first rule is to check very carefully for water intrusion, especially around windows and the cab-over.
Good luck finding your new to you rig.
