I have a 3.8 age gap. I would say:
Get used to bf anywhere ... I used to bf DD2 sat on the loo whilst DD1 was having her bath. I could then put her to bed whilst DD1 was looking at some books/playing with toys, then put DD1 to bed.
Washing on every day, into tumble dryer, fold and smooth ... iron the bare minimum!
Try to find a way to do something with DS1 just you and him. They need time with just you without the baby.
The baby can be strapped into a bouncy chair (if it is a lie-back one) and put on work surface in kitchen out of harms way and so you can still get on with stuff.
Simple dinners - roast chicken, jacket potato, salad one night, left over chicken the next etc
I established a bedtime from day 1, mostly as DD1 was going to bed so why wouldn't I put DD2 to bed just before (also can't imagine DD1 would be v.impressed with her little sister being able to stay downstairs). Of course DD2 was usually up a couple of hours later but no big deal.
I bathed them together - when DD1 was really little I used an over-the-bath baby bath, when she was a bit bigger (but still maybe only 4-5 weeks) I used one of those bath chairs. Was always good fun when she did a poo ... "everyone out everyone out!!!".
I found it not as much of a shock 2nd time around as we were already in the chaotic world of kids and parenting! Things like weaning are so much easier ... I remember making up ice cube trays full of stuff for DD1. With DD2, if I was cooking peas, carrots and potatoes for DD1, I'd mash up some for DD2.
Go with the flow and you'll be fine.