What do you use to edit???

I currently have a Macbook Pro Air which was fine when I just edited a few videos for work, now I'm finding that I'm getting more into and looking to build a semi professional setup that a lot of the apps I use are just to powerful for my machine when multitasking. So I have to sell my laptop to get something else.... This is where im confused...

I use my laptop for portability, but only around house

Think if I got a Mac Mini (upgrade it obv) and a iPad mini I'd lose something? Or do I jus save and get a Macbook pro and continue to mirror it to my Dell monitor?

I started with a song Vaio laptop with reasonable spec, it choked terribly with the 5D MKII files even after conversion with mpeg streamclip. I gave up on that ever working to any standard and went the iMac+FCPx route, I have a 27" 3.4ghz i7 with 256ssd drive for software 24gb ram and there's us 2gb of ram on the video card. I can tell you that this set up is working great, the screen is wonderful and nothing chokes it up, nothing!
Now I don't know if its the beefy machine or FCPx that works so effortlessly but it does. I'm quite sure a well speced MBP would do the job very well though

You'll get better performance out of an upgraded MacBook Pro than a Mac Mini. It'll be a good fcpx machine and you'll also have the portability of your Air. I use a 13" MBP to edit, and I've got multiple friends that have the nicer 15" MBP models that do really well with it. You can always add an external monitor for more screen real estate.