Understand why a baby feeds more at four months and it will help you to make your decision.
When a baby goes through a growth spurt they use up more calories. Their body cues their apetite before the growth spurt to cause them to take more milk. This has two affects, 1. it gives them the extra calories they will require and 2. it tells Mum that baby is going to go through a growth spurt and "please have some more milk ready for the bigger baby".
Often what has happened is that stressed and worried parents have gone to the next baby clinic or booked in with their HV or GP convinced something is wrong with their baby. GP or HV says they're hungry and recommends starting solids. They go home, go shopping and start weaning. Within a few days the baby starts sleeping through, magic!
On the other hand if they had done nothing the baby would have started sleeping through then anyway because they were over that phase of this growth spurt.
Think about the last time you went on a diet. Did you use green top or blue top? Did you cut back on icecream or vegetables?
Reverse it. By giving your baby rice or vegetable puree because "they're hungry" you are giving them less calories, in the same way you cut back the blue top and icecream on a diet.
Even if you are not interested in babyled weaning, the research is there to show how a baby developes.
WRT sitting up and feeding. From before a baby is born every part of a their development happens in perfect order. There is no blood supply until after you know you are pregnant so that you don't accidentally harm your baby etc. After they are born they develop in order to take them from one stage to the next. Think about their eyesight, they start by seeing far enough to gaze adoringly at Mum while she feeds them, then they can see further to encourage them to lift their head when they lie on their front, then to encourage them to sit up etc. Their development towards weaning happens to allow them to sit up so they have a lower risk of choking (gravity), their grip coresponds with what they can safely chew, swallow and digest and they don't have a pincer grip at first which means they can't choke on the smaller things.