Hi and welcome to the forum.
So sorry to hear of the job loss and ill health.
You are doing the right thing by addressing your debts and your creditors will not be worried that your have been spending, particularly as the circumstances that have brought you here were unforeseen. You can spend redundancy money on whatever you like prior to an IVA. It is the creditors outstanding at the moment who are the priority.
As to your wages, your payments should be done on basic pay, anything your earn over that is usually split 10% over basic pay plus 50/50.
The forum is also here for any advice and support you need.
I would suggest that you speak to a couple more companies before making a decision. Either contact one of the experts who post on here (details can be found under the 'Ask a Question' link on the left) or visit
www.iva.com for a list of companies and reviews and speak to one or two. The advice is free and impartial.