Alright, I see a lot of these kinds of topics getting posted about projects that, unsurprisingly, never make it into existence.
Despite this, I'm still going to post on the assumption that you are actually serious about this. Please understand that the following criticisms are intended to be constructive. I don't want to come off as sounding like I'm stating that your idea is dumb.
1. The Setting
Honestly the setting seems incredibly bland. "Humans spread throughout the galaxy, now they're fighting each other" is just about as generic as "Humans spread throughout the galaxy, now they're fighting each other as well as a new alien race."
In all seriousness, the galaxy is big. Really big. Enormously huge, even. In 600 years I doubt we could even populate an appreciable fraction of it. I understand that large settings are 'in' these days, but the only way I can see you being able to fill this is by procedurally generating the vast majority of it, thus creating bland 'everywhere is basically the same as everywhere else' that exists in real space, but rarely exists in fictional space.
In short: Setting needs a lot of work to be interesting. I suggest you check out some of the fiction writer's resource aids on the web, they should be of help in laying out your setting properly.
2. So... this is going to be like EVE Online? Except your spaceship works more like a mech from mechwarrior? This is how I'm reading this.
I'll break this apart a bit at a time.
MMO - Hard to do! To properly run an MMO of the caliber you are suggesting takes a lot of startup capital. I'm not even going to go into the fact that you really need a team of people to get this kind of thing off the ground to begin with... although...
Coders - Are you the only one? What about modellers, texturers, sound-effects guys, and so on? If you're going to make this work, you need a team of people. I don't want to sound like an asshole here but if you're running a project here, your best bet is to have something to show off before telling people about your idea and making promises. People will be more inclined to join your project if they can see there is a main driving force behind it, and that stuff is going to actually get done.
You also need a plan.
The Plan - A project plan that is. You need to write it up, in detail. This means details about how each aspect of the game will function, details about every object that's going to be in the game. It's basically an enormous to-do list stapled onto the back of a detailed game concept. By having a plan like this, and sticking to it, you minimise the prospect of feature creep - a real danger on any project.
Gameplay - You need to determine how the game is intended to play. Are you going to go a route similar to EVE and allow players to establish their own factions? Or will you have existing factions like governments and semi-detached groups like pirates available? The game currently sounds like you intend it to be heavily combat based, so you need to figure out reasons for folks to fight each other.
You say that tactics will be very important, and that survivability and armor will both be very high and weapons are going to be rubbish. If tactics are important, what do the latter promise except to possibly draw out conflicts? Speaking of which, in space (which is empty), what kind of tactics are you suggesting be used?
I'm sure that I've missed some stuff that others may pick up on, but the sum of my suggestions is: Right now all you've got a very general outline for a game, with a very generalised plot. If you're going to move ahead with the project, you need to improve all of the above (at least), or it just won't work.