Be aware that "main stream" laptops can tend to cause problems as they often use cheaper components that sometimes do not deal well with the high stress loads of DAW use.
USB can work as an interface, though other options are generally better. One company, RME, does produce very highly regarded USB interfaces, but those are not cheap. They are known for good drivers, and for live stage use, having something that rock solid could be a plus.
As stated before, I would urge you to contact a company that specializes in computers for music production/performance.
Another option, though not one I know much of anything about, would be to get something along the line of a portable cube computer. A DAW maker might very well offer something that would be robust enough, for less money than a laptop, and then you could add a dedicated LCD monitor.
It would also be a good idea to continue to do more research before purchasing anything. The last thing you need is to discover all kinds of major problems - that perhaps cannot be fixed - after your purchase. For casual/hobby use one can manage to use all kinds of non-optimal equipment. For what you are going to be doing, you will not have that sort of error margin. You need something that will do what you need, and work well.
Unfortunately, the only companies I know of or have dealt with are in the US, and that will likely not be of help to you. The one I have purchased from in the past is ADK, and they do offer a specialized laptop.
