Firstly bin donors off entirely. Right now if we wanted to setup a new political party it would be cost prohibitive. That to me denies democracy. So we need to find an agreed approach to funding prospective MPs - perhaps a state funded cap - now you need to limit the number of applications so as we don’t bankrupt the state so prospective MPs needing to have 1000 signatures backing them to appear on the ballot (or whatever number makes sense).
I’d then go further and make everyone campaign on an independent ticket - once elected they can form co-ops with other MPs. As an independent when you’re out campaigning to be elected you’ve got to pitch your local and national ambitions rather than the current franchise vote…oh I’m voting for x as we always vote Labour/tory/etc.
Second jobs are probably going to always be needed as you have practicing doctors etc who need to do some minimum amount of work. You could potentially limit the professions.