I don't get paid per treatment, just hourly, but expect feast or famine. In my personal experiance I've never had a problem getting enough hours and have plenty of PTO banked up if needed.
I work 4 days a week and take call on Sunday, your schedule will be site specific.
As for when you can go in for a single treatment, that will depend on the doc you are working with (they have to see the pt while on the machine so do they want to come in early or stay late), the condition of the patient (if K is high you better get there before ER doc gets excited and orders kayexalate), what else is going on with pt (d/c after dialysis, procedure before or after dialysis). Rule of thumb, never put off a treatment that you can do now because you never know what later is going to look like.
PTO and sick day benefits I guess are site specific, I get PTO. I don't have any experiance with 1099, sorry.
I usually work by myself with 2-3 patients at a time, I would love to have a tech but that's been a non-starter since I've been doing acutes. If you have a tech, you'll need to justify it by taking on more pts per shift.
I try to call for pts at 0800. This gives them time to have breakfast, labs resulted and docs are coming in. I am on call from midnight to midnight the day I work, but very rarely get called in. I may have to stay late if there are a lot of patients, but usually don't get called in.