you can do it however you and your baby feel you want to do it. by waiting til they're 6 months you don't have the same worries as with a younger baby. if you have allergies in the family then you would be more cautious as you would be with puree. however, most of your annabel karmel and other weaning others still start their weaning plans from 4 months so suggest you introduce food very very slowly, as you described with one food for 3 days etc etc. but after 6 months you don't HAVE to do this. however, if you feel more comfortable doing it this way then that's ok too.
with blw the idea is you just hand over bits of your food as you eat it. so say you're having sunday dinner, you put a potato, a carrot and a broccoli floret on your baby's tray and let them get on with it. in reality you might start off by deliberately cooking potato or carrot in chip shapes which are easy for baby to pick up. but again, you don't have to, just give what you're having. you must of course be careful of salt (no more than a gram ish a day).
they might not eat a lot of it, that's ok. it's not like the 'puree route' where you would maybe be building up from a teaspoon, to an ice cube, then three ice cubes. you just offer bits of food and as your baby gets better at handling it, you offer more, and offer different textures and sizes of foods. their main food is still milk so it doesn't matter that they don't eat much at first.
then slowly but surely they get better and better and can pick up even small things like peas..this develops as their body becomes capable of handling a pea without choking on it. until then they will only be able to grab food with their fist, so it has to be biggish things, or things in chip shapes.
does that help?