how many 5* units you usually net from 140 orbs?

Depends a little bit on how many orbs you pull per round, but if you don't run unusually good or bad, I'm pretty sure you get 2.

Its just a matter of chance, used about 250 orbs on a Legendary banner and got six 5*s.

1 or less, most of the time I snipe for 1/2 colors.

On average if you don't colour snipe for a specific unit, it'll be about 70 orbs per 5 star on average.
ON AVERAGE

2 is the statistically expected number, more like 1.5 if you're sniping.

It depends on what colors you're going for and how many focus units share that color. I'll say I used around 115 orbs this morning and got no 5*, but I've also gotten 5* from the free summon on banners before. Pity rates make it a little difficult to calculate averages, but you can mess around with Summon Simulator a bit and see how many 5* it gives you.

From what i remember with that many orbs with bad lack i could get nothing but with good luck i could get up to 7 units doing a full rotation

2-3 if Im really lucky 4-5

Usually about 2-4

0 for me lately.
Although, I guess you would "expect" one.

Generally 2, maybe 3. Any more than that and you have really been lucky.