No known maximum size exists yet. Users have reported succed with 2GB cards, but since the detail maps of all the continents fit on a card that size (and becuase they get really expensive as they get larger than that) nobody has reported trying anything larger.

No. Flash memory is a lot faster to read than it is to write. The classic case where it matters is a digital camera where you may want to write a couple of MB (hi-res picture) a couple of times a second. Designs that are dominated by reading the memory (i.e. mp3 players or GPSes) instead of writing to it don't really benefit from the improved write speeds .

No Explorist model has an antenna jack. You may use a reradiating GPS antenna Unless you're using it in an enclosed area like the hull of a boat, you're unlikely to find this necessary.

Magellan sells windshield plunger mounts. Some people report success with vent clips or cell phone holders in their car such as the Radio Shack 17-548.

Gilsson makes the Gilsson MEN GPS case.

Cartom Explorist cases