I have to echo Pach - the Chiltern Archery limb exhange program is probably the best deal you will ever get.
You pay £50 get a set of KAP limbs at a weight they help you with and then if you exchange within 6 months then you can change the weight, up or down without anymore expense. It allows you to have lighter limbs initially and develop form and then move up in weight in stages so you maintain form without the expense of having to buy new limbs every few months or going for a far too heavy limb and the wrecking your form. Whne you are ready to move to more expensive limbs you get money knocked off as well aparently, I am still to make the move.
As for which riser, well get along to a retailer with a good selection and actually have a look at them. Colours, shapes and sizes all make a difference to you, you may love the look of a bow on the internet but when it comes to the real world you might hate the feel of it.
When I bought mine I went on my own talked to the guys at Chiltern Archery and with a set budget actually went through the different options and packages I could get.
I was really pleased with going to a bricks and morter retailer, you know where they are. You can get a feel for the people and if you listen to their advice and suggestions then you cannot go far wrong.