I haven't set up a charity but I used to work for the charity regulator, and later worked in government on the Charities Act. Whether you set it up as a charity depends on whether its aims and activities are charitable.
It might be simplest to think how you would expect to raise the money to set up and run the business: are you basically aiming for this to be a business, generating all its revenue from the people staying at the retreat, or are you basically proving respite for the clients and would hope to fundraise from charitable foundations and other organisations which might fund a charity (eg local authorities?).
On the salary point: if you think about it, many many charities have paid employees (Oxfam, British Heart Foundation, plenty of local charities), and so it is perfectly legitimate for your running costs to include a salary for the director (ie you). If you were applying for grants to fund the organisation then it would be completely normal to include salary costs within the grant application.
Have you thought of trying to find whether there is already a local or national organisation (probably charitable) which does something similar, which you could piggy back on? Much much easier than setting up something from scratch. How about contacting RNIB or Action for Blind People for advice?
There is some useful advice on the Charity Commission's websitehere (they are the regulator of charities).
The National Council for Voluntary Organisations might be able to give you more advice. They have a useful website, and a helpline. Info here. Also google your local Voluntary Service Council - they may be able to offer local advice.
Hope this helps a bit; if you have any other questions then I would be happy to share anything else within my competence!