I still think it'd be near impossible to get anything Erf-like written from scratch, so there's another idea which might be worth thinking about, namely a branch of the battle for Wesnoth.
The game already has:
-hex grid, turn based strategy
-support for all kinds of units, including flying
-towns which are really Erf-like (i.e. the town isn't a single structure but rather a group of hexes each of which is treated separately). It's a matter of a little work to make different kinds of town hex (i.e. walls, etc) which would give defenders different bonuses
-It contains a lot of the things that you need for _any_ such strategy (graphics, music, user controls, online play, etc)
-there are many different units (different for each side) who gain experience and level.
-units are purchased using ONE currency (like shmuckers in Erf), so there's no woodcutting, stone or other mining
The biggest thing is that it already supports user-made campaigns with incorporated story. Hell, just sticking Erf unit images and making a short campaign on the original Wesnoth would be a lot closer to Erfworld than any from-scratch project could get within a year or three.
So really, Wesnoth is such a good choice because there's so little in it that actually doesn't fit in an Erfworld setting. Most of what we'd have to do is add stuff, most notably stacks. This is actually one of the few major things which are missing, and once stacks are handled the path would be clear for dealing with mounts, leadership, casters, etc.
Edit: I forgot to mention that Wesnoth also has a fully functional AI, which is something that can be horribly time-consuming to get up and running (let alone to get right). Admittedly it's written in C++, which is much harder to be good at than Java for these kinds of applications. Still, there are a few other projects in sourceForge that are Java implementations of various hex-grid turn-based strategies (though admittedly most of them are WAY behind where Wesnoth is at right now). Picking up any of them to clone will probably save months of development.
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