Well fighting games have the chance to have a sweet little program called GGPO which does all the online for them. Big editors are reluctant to use it (the 'I didn't make it, therefore it sucks' mentality), but I'm not. I'll have to dive into the pages of code it consists of to optimize the compatibility, but it's not as bad as if I had to do it myself.
But yeah, there are a couple big features I consider optional (the story mode, mainly, the online comes close and the amount of characters is very likely to change as well), and I will not work on them until everything else is ready. As I said, I put the emphasis on the quality of the content over its quantity.

The game, in its early stages, will look a lot like what you've described, though. But I'll try to be smart and make it so it's easy to just 'add more stuff'.

The price model seems wrong. If your target audience are casual players, monthly fees + pay2win don't work very well together. Monthly fees make the newer players flee, and pay2win makes your more faithful players flee. A solution would be to have a free 1 week trial of the game, of course, but most casuals will download the game thinking 'I'll just delete it once the free week is over', unless their friends make them stay.
There are several types of casual friendly MMOs out there already :
-social games and some mobile games, which make their money out of either ads or buyable powerups (aka pay2win without the competition).
-a few free2play like transformice, dofus etc...(the other free2play making most of their money by being addictive, they don't really belong to the casual friendly category) Which usually make their money out of premium memberships which unlock content.
As for locked areas every month that you can unlock for money, that's just another form of monthly fee, except a lot of work goes to waste each month, when you delete the area. And it's a lot of trouble to design (When you delete the map, where do the people that are there or were there when they disconnected go ? Do you have a main area where you end up whenever you log on ? Cause that greatly reduces the incentive to explore, to begin with) I know dofus has that : most higher level areas are premium only, and have greater rewards in them, as well as locked content such as pvp arenas. Idk if their premium membership is for life or monthly.

As for the game itself, I couldn't tell, but that's mainly because the main history plot and art theme you've revealed us so far is 'you're a combat dog in a forest full of other combat dogs'. No classes make sense, they add more diversity but that's not what your target players look for.