If you want reliability and comfort, I wouldn't get a laptop. Cramming all that electronics into a small thin case with poor airflow is not in the best interests of longevity. Used occasioanlly they can last quite a while, but they don't tend to stand up well to daily use and being left on, especially the batteries.
The screen and keyboard will amlost certainly be inferior to what you're used to, in size and comfort - these computers are designed for convenience and temporary work- on- the- move, not as a permanent solution.
Upgrading is also trickier and more expensive. Getting into a standard PC is childs play but opening a lap top is complex, fiddly, time consuming and usually requires then service manual. Off- the- shelf parts are not really an option, as each maker uses their own drives, batteries, fans etc - $$$. I know because I've done it a few times and it's no picnic!