Hi Fugazi and welcome.
Firstly, who is the company you are with, and have you spoken to them about an IVA?
If you own your own house, you would not be expected to sell it, but you would be required to release a portion of any equity in the 4th year of the IVA. Your car should be fine unless it is of great value.
You would pay across your disposable income after all your priority bills have been paid.
As you say, you would be protected in an IVA and your creditors would be bound by it and couldn't put on interest or charges.
If your DMP company can't help you, or if you wanted to change companies, visit www.iva.com
for a list of companies and reviews. Give one or two a ring and they will give you free and impartial advice about all the options open to you and the best way forward for your circumstances.