Unfortunately not. Whether you get a single or multiple Saudi visa depends completely on the visa invitation authorisation letter that your Saudi sponsor applied for and obtained. Therefore, if you would like to change your visa you must ask your sponsor to apply specifically for either a single or multiple when they apply for a visa authorisation letter.

This means that you are applying for a visa from the Saudi Arabian embassy in London. Therefore, if it says this on your visa invitation letter, you cannot apply for a Saudi visa with this specific invitation letter from any other city (e.g. Paris). Equally, if it says 'Paris', then you will not be able to apply for a Saudi visa in London and will need to find an agent abroad.

As far as we know you cannot. You will need to apply for a new visa from the Saudi Arabian embassy from your country.

Yes. As long as you have legal residency in that country and your visa authorisation letter from the Saudi Foreign Ministry says you are coming from that country (e.g. 'coming from Paris'), then you will be able to apply from that country.

You need to stick your old passport to your new passport when you travel to Saudi Arabia.

The requirements for both types of visas are the same. However, the nature of the visit is different. If you are going only for a business meeting and hold an administrative title, you will need to apply for a commercial (business) visa. If you hold a professional title (e.g. training, engineer, accountant etc.) and you are planning to go to Saudi Arabia to do some work or training, then you need to apply for a work visit visa. Please note that to get either one of these you need to inform your Saudi sponsor to apply for one or the other depending on the nature of your visit.