are generally very reliable, and every bit as good as a desktop, with a few caveats..........
1. The enemy of most laptops is heat, and you should guard against sitting with it (you've guessed it) on your lap. This can restrict the cooling flow of air under the casing, and in my experience can lead to overheating in some cases.
2. The keyboard will be smaller, and not quite as easy as a desktop keyboard to use. If you are in the habit of typing lots of text you will find a laptop slightly more tiring to use over a long period.
3. As you have said, you'll not be able to do much by way of upgrading - apart from adding RAM, which is usually very easy - although you shouldn't need to do much anyway.
4. It's easier to damage a laptop by dropping or knocking it, and if you make it your main machine you'll have to take great care with it - a damaged hard drive is no fun if you have no other machine.
Having said all that, more and more people are using laptops as their main machine. I use mine a lot, and in fact I'm typing this on it. I use it to edit the forum via a wireless network when I'm in my home office, and in the summer it's good tom be able to sit in the garden and work on the forum. I have owned many laptops over the years, and today's models are light years in advance of the older machines. A good laptop will easily do everything a desktop can do, and the portability makes it a joy. Go ahead with your plan - provided you pick the right machine (and accept that it will cost a good bit more than the equivalent desktop) you'll have no regrets. Well cared for, your laptop will last as long as a desktop, but be prepared to operate it on the mains transformer a lot - battery life isn't anything to write home about.