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regarding the recirc, think of it this way. If you dont have a recirc and your water in the pipes is room temp, it needs to travel first from the hot water heater through the pex to the manifold and then from the manifold to the specific faucet. In a large house, it can be 80-100 feet easy. The tubing from the heater to the manifold is not 1/2 inch either. I dont know the exact size, but I am thinking 1 inch (I havent gotten that far with my plumber, since I have not started construction yet). That thicker tubing holds much more water per linear foot, so you need to move A LOT of water in order to get hot water to your faucet, so can actaully take longer to get hot water compared to a traditional setup. If you use a recirc, the manifolds will all be on one big loop with a recirc pump, rather than homeruns from the hot water heater. This way the hot water is always at the manifold and only needs to move from the manifold, which is close by and through 1/2"(or 3/8") tubing, so you get hot water quick. Without anti scald devices, you can scald yourself with or without a recirc, it will just scald you faster :-) I havent gotten to the brands and pex type yet. I only know that I will be using PAP in my radiant system. Be sure to let your plumber give you prices too. They can get some good deals from their supply house and better to give him some profit than some faceless website if the pricing is close.

I'm doing the same at my home now. I am going pex all the way, except for the stub outs for the fixtures. Pex to copper is fine, but I would suggest that you eliminate the galvie entirely. You do not have to run the "home run manifold system". With my lay-out it is better. YMMV. You can pipe it conventionally. What I like about the manifold system for me is that I am running small diameter tubing to each faucet. That means I will not have to wait as long to get hot water to a faucet. If you look at the cross sectional area of 1/2, 3/4 and 1" tubing, they are .19, .44 and .77 sq in respectively. That all equates to volume that you have to move out before you get hot water. Just something to think about.

Although there are exceptions that prove the rule, in general all "PLUMBING" requires a permit but "Maintenance Plumbing" does not. The question then becomes, what constitutes "Plumbing" versus "Maintenance"? Maintenance is defined as maintaining an existing system in its original design and configuration therefore if you are replacing the original piping with the same size of lines and maintaining the same physical layout of the piping system you generally would not be required to pull a permit, however we must use a bit of caution here. In some jurisdictions if we are replacing pipe, valves or fixtures with exact like kind replacements it is defined as maintenance and no permit is required, but if we are switching to a different type of pipe, valves or fixtures such as replacing copper pipe with PEX they may require a permit. If we are adding additional fixtures or altering the physical location of the fixtures which would require altering the original layout of the supply and DWV lines that would technically be defined as Plumbing and generally would require both a permit and inspection. In general PEX is much easier to handle than copper but PEX requires a much greater attention to detail than copper or CPVC. By example, copper or CPVC requires a hanger within one foot of any major change in direction and one hanger for each 48" of linear run, but PEX requires a hanger for every 38" of linear run. (some jurisdictions require hangers every 36"). When installing hangers for PEX the hangers must allow fo ra greater physical movement of the pipe and the codes define a specified percentage of slack to compensate for thermal expansion and contraction, PEX must be afforded protection from both direct and indirect exposure to UV light. In some jurisdictions they require that when PEX is run through a stud bay, the underside of the stud bay must be covered with black plastic sheeting or other suitable means to prevent indirect UV light exposure. Color coding the hot and cold water lines is often done as a matter of convenience but i am not familiar with any specific code requirement to do so. Having said all of that, we must go back to what was mentioned in the previous reply. All jurisdictions have differing rules on permits. By example, in our municipal jurisdiction we are required to pull a permit for all water heater installations whether it is new or a replacement. On the other hand, in the county outside of our municipal district you can build an entire house from the foundation to finish and the only permits required are to drill a well, install a septic tank or attach the driveway to the public roadway.