The reliable way to hire a tradesperson

Hello, I'm planning to replace my front door and rear french doors. Should I be looking to hire someone who will replace/fit the doors after acquiring the doors myself, or looking at someone who I would also acquire doors from and can measure up in advance?

I have an external socket which is supplied by its own circuit from the distribution board. I have a pool heater which requires 13A to run. I ran it last year on a heavy duty extension cable with no issues. This year it is overheating at the plug and melting the socket. The heavy duty extension cable is built for running powerful tools so should be able to cope but this year it isn’t. Any advice?

Do I need permission to remove a load bearing wall ?