#1) You should use a fuel filter for both. All it takes is a couple grains of sand to get into that engine and you're out $200 or $60, respectively. And off road cars tend to get filthy dirty with sand and grime coating the fuel tank. The only time its safe not to use a filter is in an onroad.

#2) Top fuel brand is Traxxas's brand of fuel.... They're just trying to make more money. Any good 20% nitro fuel will do. Top fuel, blue thunder, HPI's stuff, stick to the brands.

#3) I don't have a volcano (I have a Savage) but if it was possible to get any more clearance they would have done it stock. Maybe this might work though.... Take off the shocks and see if the A-Arms allow any more room to go down, and then use the alternate bottom mounting holes (they're in my Tornado, same car) to bolt the shox back on.

If I were you, I would put onroad tires on the Volcano and use it like that. It's not that durable. Neither is the T-Maxx, but it is a huge step up. (Then again, I'm comparing the Maxx to my Savage)
<br type="_moz" />