First, great idea. Second I'd recommend checking out the
C3G section of these boards. Currently there are over 700 characters with cards you can print that have been tested with the Marvel set.
For the figures, look into the Heroclix figures. They are (mostly) the same scale as Heroscape and some of the figures are great quality. You can find a lot of figures on a few of the online stores for less than $1 each and many for $0.50. Coolstuffinc has good selections and shipping isn't bad as long as you buy several figures at once. Also Trollandtoad has good prices as well.
Good luck.
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Welcome to C3G!!