Hi Marcus,
Do you have a budget in mind? are you going to tow it or berth it somewhere?
For ease of use, launching, towing etc, I would guess that something around the 16ft mark is what you're looking for. Plenty to choose from but the Orkney five20 and five90tt are both excellent and the Alaska 500 is a good boat with plenty of deck space.
You'll need all the usual safety equipment. I wouldn't go out without at least one gps and a paper chart and compass, vhf / dsc radio, (you'll need to get a licence - check with the RYA ), an auxilliary engine, life jackets, anchor and a few other bits and pieces which you can easily find out about. The coastgaurd will come and do a free safety check on your boat and advise you as to just what you should have on board.
As for the trailer, I tend to carry at least two spares for everything, 2 spare wheels, sets of bearings, spare hub, spare battery, fuses, tools...............and I look after the trailer, washing it down and stripping the hubs and cleaning and re-greasing the bearings every time it's been dunked in the sea. This might sound a bit daunting but it's all pretty simple, takes less than an hour and can save you a lot of hassle in the long run.
Let me know how it goes and I'll help you out with anything I can.
When you come to buy the boat check out
http://www.ardwellmarine.co.uk and give Tommy a call. He's done me some great deals in the past.