You’d be better off working in the business to some degree and having 2-3 guys working you could work 2 days a week and you could do that well over 65,as long as you are involved in the running you’ll get a good enough income to semi retire.
If you purchased 4 flats 25 years ago since the law change in taxes you would be giving 2 of them to the government if you decided to sell all 4 of them.
That ship has sailed people have made a fortune from buy to let’s,like anything the government soon stop it when see ££££££S for them.