I'm no expert, but we started BLW with DD a few weeks ago and we're loving it! I was fairly open minded and actually thought I'd end up doing purees, but giving her real foods was just so much more fun, particularly for her!
We actually started just before she turned 5 months, just to keep her busy while we ate, really - she was itching to join in! But there is really no rush - their main nutrition comes from milk for a while yet and at first they mostly just create utter havoc play with food.
Gill Rapley's book is a great guide. I'm sure some of the claims are a bit tenuous, but there's a lot of interesting stuff in there and it's useful if you don't know where to start, like me. At first we just gave her grabbable chunks of stuff like steamed carrots, sweet potato, pear, etc., but increasingly we're giving her bits of what we're having. Last week we even took her to a restaurant! (Great advice I saw on MN recently: take wipes, leave a big tip!)
As for the vitamins, I'm not really sure, but I think the NHS recommends giving drops, mainly because lack of sunlight in the UK means most of us are deficient in vit D, so I think I'm going to start her on them, particularly as the days are getting shorter and dingier. I'm also bf, so not sure what the advice would be for ff babies.
Sorry for the essay - as I say, I was open minded about the BLW thing before we started, but I'm borderline evangelical now! Good luck with it all and tarpaulin the house have fun!