Yeah you have a valid point regarding the umbrella company. It does offer some benefits (eg. you are a PAYE and if taking loans for car/house you can say you are employed rather than self-employed which could hinder your bargaining abilities). I do not think they help that much when it comes to finding contracts. My understanding is that they handle the paperwork and finances, thats about it.

Just put your CV out there and apply to 2-3 jobs. See the feedback you get and take it from there. I don't think previous experience as a contractor is important - that being said, having professional experience in the field is definitely very important.