To clean under the deck there is a hose pipe nozzle on the top of the deck, connect it up, turn on the water, turn on the engine and drop the deck down to lowest height, and turn on the blades, all the crud is expelled from underneath.
My Rover (MTD) ride on mower has two blades underneath, they have lasted me over three years to date.
Replacement blades are about B1200, the supplier will usually offer full service and parts.
My battery just went down due I think in part to the safety cut out on the engine that cuts off the engine every time you get off it and then having to re start it when you get back on. Standard 12v motor cycle battery fits.
I have now short cut the safety cut out to reduce the number of starts.