New to TFT, bought the pocketbox version what next?

[HeatDeath]

The Death Test box comes with counters that are a touch big for the maps you have, but is definitely a logical next purchase.

The PDFs of the adventures would also be a good next step. You don't yet have the full RPG rules (those are in In the Labyrinth) but the adventures have interestingly new and different creatures for Melee/Wizard play (especially Chaos Triads and Clockwork Tower!), and if you print the counters at 75% they'll fit the maps you have.

After that you'll want either the Into the Labyrinth book or the Legacy Edition box set (which includes Melee, Wizard, and Death Test with the bigger counters and maps, as well as vast amounts of other goodies).