Tyre wise you want yellow shumacher mini spike, the greens are ballistic buggy and are for use in the wet. Weight of a servo isn't really a issue it's speed and torque you want, xpert servos are really good, not cheap but we'll worth it,
http://answer-rc.com/uk/en/1397-xper...rt-48-66v.html is what I use but
http://www.rccarshop.co.uk/index.php...-4-8-6-6v.html would be good enough