I think your biggest problem with this is that no laptop may offer the kind of CPU power that you'll need. Running MIR requires at least Quad processing abilities to run even a modest ensemble. RAM is also an issue but it's the CPU that I see as the main problem.
I work exclusively on a 17inch Macbook Pro (3.06 ghz model with 8 Gig RAM) because I'm always on the move. And I do pretty well with this but of course there are limitations that I have to work around. Limited CPU overhead for instance. I use a combination of Logic to compose and Pro tools to mix with. And I'm using a very large VSL library.
My point is to say that working with a laptop is more than possible if you're patient to work with the limitations. But if you're looking to run CPU hungry programs like MIR I think you will need a desktop system.
Nothing says that you can't use a laptop to compose with and connect up to a bigger studio machine that runs MIR of course. That's what I intend to do later on .. to keep my Laptop is my primary studio unit, and just have it connect to bigger machines to run the VSL library through VE Pro and MIR of course.
Any decent laptop machine will allow you to run your full VSL library. SSD is a good idea, but I'm not sure if it makes such a big deal at this point for the price one pays. Just make sure your HD is a good fast one. 7200 rpm at least. Avoid anything slower. IT's also worth thinking about what kind of sample rate you want to record your music in. Most laptops will choke from trying to work at 96 khz. But if you're happy to work in a more CPU friendly 44.1 or 48 khz then you'll be fine. It may sound like a shallow point, but believe me it's worth considering this quality issue as you'll have to deal with this problem sooner or later. Higher sample rates mean way more processing power needed.