It's a long read but I suggest you read
Bill Pentz's website if you haven't already done so. There is repetition but that is to make sure people that visit to read one aspect of dust collection get the important stuff.
The DC flow ratings used by sellers is just for a motor and impeller without ducting or filters and the readings taken from the centre of the airstream where it is fastest. So in reality the claimed airflows should be about half of what they publish at best.
Keep the use of flex hose to a minimum as it has about three times the drag of solid duct. So 10' of hose is 30' of duct.
Flow through a 4" duct is about 450 CFM at best and usually less, flex even lower. The 6" duct can move about 1200 CFM and that's why it is recommended if you want to grab the fine invisible dust you can't see with your eyes. Going from a 4" to 6" pipe will still only flow max 450 CFM in either direction as the 4" is the restriction. So stay with 6' all the way to a machine. If it has a 4" port and you can't/won't open it to a 6" then take a second 4" pipe and locate it at or above the machine to scrub the air around the machine. Actually you need three 4" pipes to flow the same as a 6". You also need to open a machine enough to allow air into the machine or the air can't get out. Two to three times the area in as out. So don't try to seal up a machine cabinet thinking it improves it.
A DC when not flowing the air has its highest static pressure and when wide open its lowest static pressure. As you vary the flow you vary the static pressure that can be plotted as a performance curve. That curve is useful to tell you how much flow you will have at the end of a ducting run. Unfortunately you don't get those performance curves from many companies. The more you add to the system affects its ability to flow air. So the length of ducting, elbows, flex hose all reduce the static pressure thus the flow through the system and dirty filters reduce the flow further. As long as there is enough static pressure left over after all the restrictions are added up you have flow. If you add too much it won't suck adequately. Adding a cyclone or separator adds more air restriction, the amount depends on the design. The better design like a Bill Pentz / Clearvue or its imitators will have a loss of a couple inches of static pressure. A separator lid/box as much as 4" or 5" of loss. So what I'm trying to say is be careful adding stuff to the system if it isn't correctly sized for it. From the little I know of cyclone design that Grizzly add on cyclone will have more drag and poorer separation than you would like.
At some point someone is going to tell you using two 45º fittings is better than a 90º elbow. That isn't true if the 90º has a 1.5 radius or bigger.
See page 54.
Using an air scrubber to clean the air means unless you are wearing a mask all the time you are filtering that dust with your lungs. It hangs in the air for hours. Better to put the money towards a bigger DC with better filtration and capture the dust at source.
You will also see people using a cheap fan type anemometer to prove they are getting huge flows with their system. They are inaccurate and give much higher, 30%+, than the actual flows. A hot wire anemometer or pitot tube type give more accurate results. They have to be rated to handle the airflows found in DC's.
A bell mouth hood is the best shape for capturing dust as at the end of a duct at the lathe or the attachment to a machine. You can get as much as a 5% to 10% flow increase compared to a bare pipe/hose. It is better than other shapes like cones etc. A 6" bell mouth video.
If you really want to learn more the best forum is a part of Woodwork Forum, an Aussie site. Lots of good info in it and the moderator is very knowledgeable. I think you might have to join to see the pictures, I can't remember.
https://www.woodworkforums.com/f200
If you want clarifications or any more info just ask.