As stated draw it out, to scale, measure the distances and always buy 1 or 2 more fittings than you think you need.
If you dont care about looks then standard schedule 40 PVC fittings are the cheapest.
Put unions in, this will make maintenance, or any reason you need to remove the plumbing so much easier.
As for bulkhead size, well it depends on the size of the holes you have. Also this depends on if you do schedule 40 or schedule 80 bulk heads. Schedule 40 are usually ABS where schedule 80 are pvc. Note if you get ABS, you will need an ABS to PVC glue which is different than PVC glue. Or you need to do a screw in fitting as an option, but those tend to be more prone to leak issues than slip fittings. BRS has a chart that shows the min and max hole size depending on the bulkhead.
If you are planning valves, gate valves are the best option long term, ball valves will work in some occasions, but gate valves give better flow control and are less likely to get stuck long term.
Once you have everything lay it out and dry fit. measure 3 times, cut once.
Also know that each fitting has an internal stop, so if you measure from one fitting to another, there is probably 1-2 inches extra that goes into the fittings. Typically when dry fitting, you dont get the pipes together as far as when you are gluing, so that pipe you cut exactly to 2' may only by 1'11" when fully seated into the fitting.
As for gluing, apply glue to both the pipe and fitting, going around a few times with the applicator is recommended. Insert the pipe and give a 1/4 twist and hold for 30 seconds. Wipe off the excess glue.
As for where to get the fittings, lowes, homedepot or whatever you have locally is probably the best for standard schedule 40 white pvc pipe and fittings. I went with a blue/black/grey color and had to order everything online.
