I'm actually at the very start of doing this myself.
I'm currently in the Himalayas in India after starting in Mumbai about 3 and a half weeks ago and working my way up North. My plan is to travel India for 2 months, before doing Nepal/Burma/Thailand/Cambodia/Lao/Vietnam within a month or two, then Hong Kong and Beijing before going to Japan and then finally I've got a 12 month working visa sorted for New Zealand from December.
Part of the reason I'm doing Asia is I did some backpacking around Europe when I was younger, but it is also much cheaper. For example, in India you can easily live comfortably on £500 per month. I think South East Asia may be slightly more expensive but not massively. For me the most expensive place will be Japan and then setting myself up in New Zealand, although thankfully I have some family over there that have offered to put me up while I find some work. The impression I get from them though is that it is very easy to find work in NZ at the moment.
I was in pretty much the same situation as you, no wife/kids/mortgage and I was becoming disillusioned with life in the UK so I decided to get out there and see some of the world while I still have my health and my freedom.
I'm not regretting it so far. Don't get me wrong, I have a big of a love/hate relationship with India but it's more love than hate. There have been a few things that are a bit of a culture shock, but if you're an open minded person (which I'm sure you are if you're thinking about doing this) then you'll find that's nothing more than "Oh, that's a bit odd."
As for my planning for it, it was very limited. I needed to get a visa for India in advance although I believe that has just changed and you can now get an e-visa for big entry points like Mumbai. Apart from that all the other countries are visa-on-arrival with the exception of China, although I can get into Hong Kong without a visa and get a Chinese one from there.
I literally just booked a flight to Mumbai and did the rest of it on the fly. It's easy enough to get around and you meet other travellers who can help you with your plans. I mean, when I arrived in Mumbai I had no idea what I wanted to do in India except see the Taj Mahal and Golden Temple (both of which I have done now). The place I am currently staying is the exiled home of the Dalai Lama and it is absolutely stunning. I probably wouldn't have planned to come here on my own reading a Lonely Plant guide, but after speaking to other travellers here I am, with some other stops along the way I wouldn't necessarily have visited but am glad I did.
It's a bit of a gamble to leave with little to no plan and I was kinda bricking it the last couple of days before I left but I'm really glad I did now. It's one of the best things about travelling alone that you have so much flexibility to do what you want to when you want to, so don't be afraid of leaving without a major plan of what you're going to do when you arrive. Even if you did plan everything out you can guarantee you wouldn't stick to it.
Go for it, I'm sure you won't regret it. I'm not. Any questions please ask.
Incidentally it was this or South America for me but I decided on Asia as I felt it was a bit more safe as a solo traveller. I'm not sure how true that is though.