The 3 year old can probably do quite a lot - I remember vividly my (then) 3 year old making "lunch" for herself and me when her little brother had a vomitting bug - she made jam sandwiches on pre sliced bread... bit cack handed but still lovely, and it made me cry at the time (in a good way) :o
TBH the key is to be slightly lazy and not too house proud - like a lot of things with young children its less stressful if you aren't too uptight about mess existing temporarily or not so temporarily - and get the kids to help tidy / wipe up!
We have a very stable, solid wooden step stool with two steps up to the kitchen sink - my 5 yo still uses it but it has been used by all the kids since the age of about 18 months under supervision and with little to no supervision by 3 (and by me to put things we rarely use up on the top of kitchen cupboards, it also doubles as an actual stool sometimes) I would recommend that.
I know of nurseries that do drink stations and I did when I was a child minder, but I've never done it dor my own kids - our preschool does it though and it works well. They also get their own plate and cup out of a cupboard at snack time and have to wash it up afterwards (special little low sinks though).
What really helped me when the kids were small was having a bottom cupboard as a "children's cupboard" containing plastic cups, beakers, plates and cutlery which they helped themselves to. They were then able to use the step stool to get a drink of water, and the fruit bowl was always within reach, as was the kitchen roll - you spill something, you try to clean it up then ask for help. Nobody's cross as long as you help clean up and let a grown up know so they can check its all gone.
It absolutely is more trouble letting them do things for themselves than doing it yourself at first, but it really pays off.
Absolutely let the older 2 dress themselves if you are not under pressure to be out of the house promptly - another thing that really helped me was setting up their cupboards with things in little baskets and only special occassion stuff on hangers, so they didn't have to pull things down. I always let them choose their own clothes - much more motivating. We've always had a nobody downstairs til they are dressed rule, which also motivates the getting dressed and stops it dragging out over the day (though we have relaxed that at weekends now they are older and can just be sent up to get dressed alone).
Good luck - its worth it. You have to unclench about mess and time though :o