I'm in a hurry, so I might come back to this later, but I have a 110 I plumbed thinking I wanted to buy the smallest return possible (I was really trying to keep the power to a minimum where I could), so I put in oversized return plumbing (mostly 1.5"), and I also oversized the drain plumbing (mostly 1.25 in a beananimal set-up).
I'm sure if I worked out the kw-hrs saved vs expense of larger plumbing, I lost a few $'s going bigger than 1". But I didn't keep good track of the fittings I bought here and there.
Speaking of that, I've worked plenty with 1" and below - I didn't realize how much harder it would be to work with larger than 1" - everything from cutting to test fitting to running sections. This meant it took me a lot longer to complete.
And my system doesn't self-purge on restart if the power has been off for any significant amount of time, say more than half an hour. Since my piping is oversized, I need a higher flow than my pump can generate to purge the air - unless I help it out. fyi - I use a sicce synchra 3.0.
That said, I don't really regret it - just be prepared.
My drain piping isn't glued in the sump and this allows some welcome flexibility. I don't run socks but I can swap out a piece and adjust some valves and run a sock for a specific purpose. Otherwise, it splits to my skimmer and ATS. Since they run opposite cycles most of the time, a solenoid valve to have full flow at each would be cool, but overkill - I don't have trouble with nutrient export. Heck - I have to dose nitrates.
I do regret not using 2 overflow boxes, and I regret close-coupling threaded unions to the bulkheads. The unions add length so the tanks sits too far from the wall. If I had just added a second external overflow box, I could have more easily set my drain tube heights, and it would be a lot closer to the wall, with a neater installation. At the time, another $90 seemed unnecessary, but I think I would have got some of that back in fittings, and the rest back in time and aesthetics.
Oh - I used a chunk of spaflex for the siphon line. I have a nice, smooth, curved descent for my siphon line from drain to sump inlet with minimal places for plugging up with a snail party. But it will flow more than I need, and getting that piece certainly added cost and time as well. In hindsight, maybe it was not necessary.
