I’m not sure if they’ll give the visa if your flight to Thailand is not out of the U.K. You can ask the Embassy and see, but I have my doubts if you are currently resident in another country.
The Visa Exempt entry has nothing specifically to do with the Sandbox, it’s a general thing. You can extend your stay by a further 30 days at immigration in Thailand.
Currently, the 45 days on entry instead of the usual 30 is meant to last until the end of September. However, given there’s no chance of quarantine ending, it’s very likely to continue to be 45 days for quite some time.
You’ll probably need an address for afterwards but don’t think they’re too fussy (apart for STV). Again, shouldn’t need a fully paid booking. The website will demand various things but you can be fairly flexible with what you put in a few sections. Embassy seem ok with it.
Depends on the Embassy you’ll be dealing with. You should be ok with flight details but not a confirmed booking at the visa stage but some Embassies are more awkward than others.
Screenshot the airline website with your name and flights but don’t pay.
You can use different flights for CofE.
London Embassy usually ok with this, don’t know about Paris.
Thailand and Switzerland are both Amber at the moment so no difference for travel to U.K. I don’t know the Swiss rules for transit, you’ll have to check.
As I said, the lists are being updated later today so keep an eye out for any changes.