Another plumbing question - durso standpipe

[Mike]

Hey guys... by now I am sure everyone knows our old 75g leaked and is being replaced with a 140g. The issue is doing the plumbing and setting up the new tank. We have a few questions and are seeking guidance.

1- We are going to attempt to use the closed loop on the new tank for circulation. We have two used external pumps that I think are both functional (assuming, but no water testing done yet to make sure no leaks). If both work and don't leak, which brand is better and which should/would meet our needs better?

Panworld Magnet Pump

Nominal output- 70 watts
Voltage 100-110v
STF. Point - 2.7m-30L/Min / 2.9m-30L/Min
Speed - 2700/ 3100 rpm
Power Consumption - 110/150W

or

Iwaki Walchem

Max Capacity 13.7 g/m (which should be 822 g/h)
Head - 8.2 ft
Voltage - 115
Amps - .45


2- Is hard plumbing better than using spa flex? Why would we want to use all hard plumbing? Is a combination hard and spa flex tubing fine? Is it best to use the purple primer and glue on the PVC joints or just snug them? If I glue everything, it does not come apart, is that a good thing or bad thing? Do I use it on where the spa flex and pvc join? If the two pvc pieces screw together do I need the glue? Any reason not to use the plumbers teflon tape on the threads? Why and where do I use the cut off valves?

3- Anything else we need to know? or any other suggestions since we are still in the planning stages?

Thanks- Mike and Kristy