My pup is 7.3 kg and although he's obviously pretty heavy and my arms do feel 6 inches longer than they used to be, we carry him everywhere for socialisation.
He is a rescue from a very bad start and has been quite poorly, so had his vaccinations delayed and only had his first one this week. Essentially this means we have another 4 weeks of carrying him until he can go down and walk.
I initially got him used to being left in a crate using the Dogmantics/Kikopup Home Alone Video method of clicker training and gradually built up the time.
He was 10 weeks when we brought him home and is now 13.5 weeks and I've just started getting him used to me leaving him for the school run.
I measure out his feeds into individual bags the evening (he is currently on 6-8 feeds a day because he has a lot of weight to gain) then use his feeds to stuff 2 kongs (one puppy kong and one medium adult kong) and at least one treat dispensing toy for him to have in his crate. I would use less toys, but he's a wimp and gives up quickly if the food is packed in too tightly - a more determined pup would probably chomp away on a well stuffed kong for much longer.
He has been on an exclusion diet of only cooked chicken, but we're currently transitioning him onto high-quality kibble, so we use a bit of both for kong stuffing and kibble in his treat toys.
This week my Mum has very kindly come and stayed in the house (but not necessarily in the room) with him while I'm school runs, so he gets used to me not being here, but he is still shut into his crate with his treat/food toys.
This morning I gave him his toys and shut the door at 8.40 and he finally looked up for the first time and asked to be let out at 9.35. He hadn't even noticed I'd gone - let alone that I'd come back! 
This is a pup that 3 weeks ago, would scream the place down if I so much as stepped out of the doorway while he was in his crate.
So yes, both leaving and taking him is perfectly doable with a bit of planning and a lot of patience and effort.