Need advice before I buy laptop for editing

Question

I have edited mini DV on a 7 years old laptop with PE 3. Now it is time for me to buy a new laptop so I can edit footage from a Canon XA10.
And buy a new video editing program. PE 12 is one of my top candidates because PE 3 has worked fine for years.
I plan to record AVCHD, 24 Mbit/s, 8 bit, 4:2:0, true 1920*1080 for maximum quality. In PAL.
No, I have never edited HD.
Yes, I have tried to check what various software companies suggest.
My editing is normally very trivial, even though I make long movies (hundreds of hard cuts in the same film). But when I do something complicated, the result is just a few seconds long. 
How powerful laptop do I need? I have the impression that the following is the minimum for editing both PE and the competitors, but please correct me if I have made some mistake.
Any Intel core i7 quad core CPU with at least 2.0 GHz
One single mechanical hard drive, 5400 or 7200 RPM (I mean SSD not necessary)
4 GByte RAM
Any graphics card with at least 1 GByte graphics memory  
I have the impression that editing HD means that one hard drive is not enough because the laptop needs to handle so much data. But how many external hard drives do I need? I want to minimize cost.
And do I have to connect the external hard drives via USB 3, or is USB 2 enough?
And one more technical question. When I edit, I see the whole project on the laptop's screen. How do I do to see only the film? With mini DV, I connect a television receiver to a camcorder and the camcorder with firewire to the laptop. But I don't know how I am supposed to do when I edit HD. Is there anything I must take into account when I choose what laptop I buy?

Answer 1

I have continued to think about my problem.
The main problem is that when laptops are sold, they are not optimized for video editing because few people edit video on laptops. And far from all of those who sell laptops are familiar with video editing, so asking them to optimize a laptop may end in misunderstandment.
So I have thought about one possibility. Buy a "cheap" laptop with powerful processor and enough graphics memory. Then tell somebody who repairs laptops to replace part of the hardware with something more suitable for video editing.
But before I do that, I must know exactly what to replace.
So I have thought about some alternatives to upgrade a laptop as painlessly as possible.
1.
I have read a short description of SanDisk ReadyCache. This is 32 GByte SSD with software. Connect it to a computer and files which are used often can be accessed up to 4 times faster than on a hard drive. Sounds relevant for video editing, but I have no idea if it works in practice. I mean, reviews are favourable but I have no idea if the reviewers used it for video editing.
2.
Replacing a 5400 RPM hard drive would not cost me that much. My external hard drives are almost full so I need to buy new ones. I mean, I can tell somebody to replace a 5400 RPM hard drive with either SSD or a faster hard drive (7200 RPM). The 5400 RPM hard drive can I then use with firewire 3.0 as an external hard drive.
3.
Unless I have misunderstood something, one can make a computer more powerful by using an USB memory as some form of memory. How much would that help in video editing?
I think this is what Microsoft calls ReadyBost, but I have never used it so I don't know.
By the way, if I use an USB memory in this way, how large should it preferably be? And how fast?
Any more suggestions than those above? And what is the preferable solution?
And yes, I have thought about the possibility to use a Small Form Factor PC, but since they are rare I have problems finding anyone. If somebody knows about a suitable one, please tell.