Welcome back to RC again m8

On the battery question the larger the mah is usually the longer run times ie a 4200 will give you about 25-30mins run upto a 1800mah which will give you under ten mins etc this all depends of course on your motor and esc setup the lower turn motors take alot of juice to perform well.Nicads are pretty old now even nimh are being replaced with lipo ans a123 batterie which offer more power and better runtimes and are a lot lighter.

On the MT take alook at the traxxas stampede a good cheap little 2wd drive MT and has plenty of part support and hopups to buy and there pretty quick stock,They also do the VXL version which matched with good batteries can hit speeds of 50mph+ [X(]

My advice is buy a quality brand like you found out with the mad truck a good company offers good part and upgrade support and wont break as much check out brands like tamiya.traxxas,losi etc

Like they say you get what you pay for so dont skimp on the kit it will save you cash in the long run