The about section sounds just too over-ambitious and loose indeed.
Even with a little research you can easily spot a lot of trouble coming.
Dynamic worlds are ok. Some interactivity is never bad, items to
collect and secrets to discover are good. But gigantic worlds where you
can go freelancing? That does indeed sound like a MMO. Don't forget
those servers are expensive to put up, and it'll take a lot of
modifications to the HL2 netcoding to support things like that. Without
a coder, the mod is dead. Without a good, dedicated coder, the mod is
still dead.
PvP, gigantic worlds, teaming up, guild-forming... what are you aiming
for? Player versus player for example brings a lot of issues with
itself. Many games just don't do this because of the trouble. Do some
research into it and you'll understand my point better.
Gaining experience, weilding two-handed swords, using magic, doing
quests, gathering items... it's all in the average RPG you get. Nothing
new there. So ask yourself the question: why, if I had the choice
between a dozen of free MMORPG's, would I play my mod?
If you can't answer that question, then your design isn't good.
I might sound negative. Perhaps I am.
However, you don't want to waste 1 or 2 years to a project that never
gets done because you hadn't investigated the effort that would be
required. You'd better spend 6 months on a smaller project that does
get released.