We did BLW with both of my girls.
I'd say they were eating decent amounts pretty early on, especially my youngest who can really pack it away. Right from the first day they both ate food but I'd say maybe around 8 months was when they started eating a proper meal rather than just trying things. But it really depends how much food you give them on the plate and whether they really like it!
Neither of mine have been particularly messy - both have liked to have a good squidge of the food but they aren't really food throwers. It's very rare that either of them spits anything out because they have always fed themselves. The only reason mine have tended to spit things is when they've stuffed too much food in their mouths... and that's happened maybe 10 times between them (they're 3.5 years and 18 months old now).
We didn't introduce foods slowly so they were both having all normal meals with us from the day they started on solids. Both liked to try using cutlery from the start but I'd say at around a year old was when forks started becoming useful; before that they mostly just used spoons to dip into yoghurt, porridge etc.
I'd expect most of a baby's calories to come from milk until around a year old, then a gradual transition to food being the main source. I would expect all children to have some part of their diet as milk until at least 2 years old, but how much of that is milk would depend on the child. My 18 month old eats as much as her older sister but she also has three good milk feeds a day, on average, sometimes snacking more on milk too.
