Myself and my fiancee are planning to marry next year here in the uk and then for me to follow her at a later date after applying for a k3 visa, we are doin it this way because its easier for her to come to the U.K to marry instead of me going there to the states.

How hard will it be to obtain a k3 visa and wot are the pitfalls we should be aware of?

"Hard" is relative. It just depends on the specfics of your case and your situation. I would start by reading the guides THOUROUGHLY and THEN asking questions. All will be revealed there

There are heaps of ppl here with spouses from the UK who can help you along the way.

the problem is that due to my criminal record that i may not be able to get into the country on a k1...would this also stop me from getting a k3 and does anyone know how i can overcome this?

Regardless of which visa you apply for, if you are found ineligible due to criminal record/crimes of moral terpitude you will be denied at interview but you are able to file a waiver for most things. Have a read HERE and in the 'Waivers Forum'.