@ElectricPaladin: Yeah, I would agree with you on the point of actually getting games in. However, I also feel that the beauty of miniature games in general, is also the collecting/painting. And also, unlike MMOs for e.g., that they can be kept as display pieces and icons of nostalgia once their time is up.
Also, I kind of guess that our OP, at this point, has already bought in. So I think, might as well get a nice "complete", well-painted, well-rounded army up, and be truly satisfied with it. For now. I think it's much better to have than having a neglected half-army sitting somewhere gathering dust, not painted, not assembled. Without motivation to do anything because it's not "satisfying". I get that sometimes...and it's mainly because I'm not "feeling it", so to speak.
Who knows, BFG *might* be reduxed/outsourced, and we never know what will happen. But not to get anyone's hopes up, but it did happen with Battletech!
Now I'm pulling out my Urbanmech Company for more 31st Century Combat.
Lastly, I suppose, one could always split one's force and/or if budget/time allows, get oneself an OpFor so that another person can play. Haha. Not that I'm encouraging it, but it's an option.
Regardless, BFG, I feel, is really distinct, with minis that really capture 40k, to me. And as for other space games, I'm not really feeling it.
As to Mr OP:
I suppose "Melta/Plasma" would probably come in the form of the good ol' Bombardment Cannons on your Strike Cruisers/Battle Barges. And "power weapons"? I suppose maybe Terminator Boarding Parties and Assault Boats...counter their formidable marine crews with more marines, and more powerful marines.
However, as an anti-Marine army in space, from a strategic point of view, if they are indeed planning for such contingencies, I think would entail countering the strengths of the Space Marine Fleet assets itself. The SM fleet is known for it's short range firepower, boarding actions and of course heavy armour.
Therefore, I'd think, load up on long range (Lance) weaponry, Torpedoes and Ordnance (Bombers), to keep them from utilising their strengths. This is usually found on the Escorts. But relying on them is a bit iffy. That's where the IN come into the picture.
In fact, it is also stated that the SM are "restricted" to such short-ranged transport-oriented ships to prevent any one Chapter from gathering too much power. And that good long-range ships of the line are restricted to the IN in order to ensure that as well. So that's where the case comes in for some good IN Cruisers like the Mars and Overlord.
