Your protein is too high.
Insofar as I am aware, protein's not going to keep him out of ketosis. I'm a fan of retarded-high protein though.
At your size, I would suggest no more than an hour-long refeed to start, not a whole weekend (if that's what you did). Sit down with a pizza and a protein shake, throw out what's left over after 60 minutes. You should find you're able to get back to ketosis faster.
keto on sunday night...not in ketosis until the next Saturday and only trace ketones!
The bigger you are, the longer it takes to get into ketosis it seems. When you've got single digit bf, it might take a day, but it looks like you're at 5 or 6 days, which makes sense. That should improve over time.
2000 daily, 20g carbs, 160g protein and remainder fat grams.
20 carbs is about a stalk of broccoli... if that's your carbs, 9g is fiber, making it more like 11g carbs. Hooray. I am a fan of fluctuating caloric intake. For example, 1500 one day, 2500 the next. I have zero proof that this does anything, but it works for me.
How long can I go without a carb up?
Well, let's say you take a week to hit ketosis. We know two weeks keto is plenty safe. I'd call it a three week total for you - at least for a couple cycles.
Is it necessary at my weight
It's necessary at any weight to keep hormones happy.
how long can I lift without losing lbm... without doing any refeeds?
There's no reason you should lose much at all, or any, provided your protein intake is high enough. I think you'd likely feel pretty run-down if you go longer than a month without a carb-up. You're your own mad scientist, though, so you'll have to dial your diet in yourself.