I have a chi X jrt, under 3kg so doesn't come much smaller 😃 He has 2 walks per day, usually about 30-40 minutes each time, but he has walked up to 5 miles with us before. He's surprisingly sturdy, took him to the beach for the first time and he was like a little mountain goat across the rock pools.
He was tough to toilet train, but cracked it by about 6 months. We got him in Autumn and he hated going out on the wet grass when he was tiny. He also feels the cold quite easily and need a decent coat in winter (but not a onesie in the house like some chi owners do
). He has also been quite tricky to train, he's not very treat orientated as he has a small appetite, but he's very well behaved and has a good recall.
Plus sides, cheap to feed, cheaper medication bills at the vets, easy to tuck under your arm if you need to go in a shop, doesn't take much space in the car, and can sleep in my bed without taking up all the space.
Negatives, hard to buy accessories like harnesses without going online, tiresome judgy comments from people all the time about how small he is, and falling over him all the time because he's so small. You also have to dog proof your garden really well, mine weaselled under the tiniest gap under our face when he was a pup.