Now this may be getting the cart before the horse but lets call it collecting supplies you will need to connect your DC to machines. Thin wall PVC will work just fine . For the best you can order metal ducts any size you want but you will also have to buy expensive connections .
A consideration many people talk about is grounding the dust collector and duct. To my knowledge and every forum I have been on and every article and book "there has never been a explosion in a home workshop due to dust collector" . Now , yes a dust collector will create static electricity which causes dust to adhere to outside of ducts. If you do want to ground you can use bare copper wire wrapped around the outside of the pipe and ground to machine and the DC.
Using thin wall PVC is easier to work with and connectors are readily available. When you put all these together you can use PVC cement but I guarantee you will rearrange the system and your shop so go with something reversible such as caulk. You can also use screws to hold the connections together but use as short a screw as will do the job to limit disruption inside duct. You do not have to seal these joints inside as you can do that on the outside of the pipe . This is not to keep the pipe together but to seal leaks. Every little air leak reduces the air flow you will get from your system and that includes all connections.
When using PVC try to keep the long runs as one solid piece of pipe, and after that the fewer joints the better. When I use 45 elbows to create a 90 I grind off that little shelf inside the fitting. Reason: you want the walls as smooth as possible because any bumps or restriction cause disruptions in airflow and reduce suction. This is why you want to reduce the use of flex hose to a minimum. Dust collectors work on a volume of air not the suction power. Dust is suspended in the air flow and disruptions can cause it to drop out and start a clog.
Now as to the size of duct " the bigger the better" is not a rule but it is better close to the DC to have larger and go to smaller closer to the machine. My Dc only starts at 5 inch so the 6 I used is overkill but not a killer as it is only 8 foot. Dust collectors do not work well on shop vac hose but that can work for small areas such as drill press or small sanders. Planners, bandsaws, tablesaws, and other large machines are bet to use 4 inch or larger connections.
Hanging the duct in the ceiling is simple and easy with several methods. Large plastic twist ties work well. Perforated metal strap will also do the job . I have made several of mine from galvanized wire. Or you can make nice hangers from wood.
I started out with what I would call a traditional blast gate made of plastic with short tapers on each end to connect flex. Note that 4 inch PVC connectors do fit 4 inch flex but take a piece with you when you buy. You can buy wire clamps made to seal the flex to connectors or buy a kit at Harbor Freight to make your own hose clamps. Recently I found a new blast gate with a spiral on one end and a shape on the other end which will fit PVC. There are many many designs of blast gate out there from plastic to metal and even some that automatically open when you turn on the machine. When you install the blast gate you will want in convenient and as close to the machine as you can get it. When you do branches off the main gates are a good way to shift the air down different runs. I have one at the top of a run and when open air goes to CMS and wide belt sander (each also with a gate) on the other side the gates at the lathes need to be closed.
More pictures next time and how to make your own gates ,