To answer some of your questions...
Parker offers a lot of lines and a lot of products, but at the top end, they are pretty much the world leader in compressed air filtration. At the top end they are also incredibly expensive. Over the years they have bought many competitors, and they have the most R&D going on. Many competitors just use technology that Parker developed or bought.
Coalescing filters are water separators. Coalescing is a method of removing water from air (or any fluid lighter than water) by forcing water particles to collide, form larger particles and ultimately drop out of the air stream. In filtration, the term coalescing always refers to a means of removing water by mechanical means - i.e. not the filter element. Any filter will stop some water, but coalescing filters usually add some sort of baffle which causes water to spin and reverse direction before passing through the filter element.
If you are going to run filters in sequence, you should run the coalescing one first and a good particulate filter after. Removing water from air and removing particulate from air are two different things, and where it really counts you always see two different filters to handle two different jobs. If you don't need things to be super clean, then a combo unit will do a fine job. By super clean I mean like a hospital.
If you are going to run a regulator, but it ahead of the filter. Any filtration is simple stuff at a low rate of flow, but at high flow rates, it can be much more difficult to accomplish. In compressed air filtration, high rates of flow are the norm, so anything you do to slow it down, do it before the filter so the filter can do it's job more efficiently.
