Let’s talk about flow!!!

Like the title says let’s talk about flow. I’m new to the hobby still. First tank up and running.
Little background on my setup
55 gal tank
60-70 lbs of live rock
Sand bed of 1.5-2” which I am gonna start replacing with a larger grain that won’t blow around so bad
48” t5 ho quad light coralife
Some cheap circulation pumps off eBay to get me started, ended up with 4 different ones. Good pumps so far but they are bulky and either to strong or not strong enough and that’s the idea behind this thread.
No sump
And no skimmer
Been doing 10-20% water change weekly
All of my test come back good and everything was great before the uglies started. Unavoidable from what I’ve read.

For live stock I have
2 margarita snails
2 turbo snails
3 blue green chromis
1 blue leg crab

Coral we have
Devils hand
Kenya tree

Ok so the reason of starting this is for the seasoned pros to help the new guys to understand proper flow of the tank. Sounds simple enough throw a few wave makers in and boom done well I’m guessing there’s way more to it then just that.

I have a few questions to start off with
Proper placement of powerheads?? I’ve seen them towards the top of the tank I’ve seen them towards the bottom of the tank. Aiming towards the glass, aiming strait towards the rocks. No consistency. I understand every tank will be different because of the aquascape but there has to be some “golden rule” to start from and adjust from there. I’m not referring to the gph either we’re still talking placement. I have moved my power heads countless times now. Tried the top and bottom, back and both sides. Top aiming down seemed to end up with dead spots and sand movement but the top of the tank moved around good. Bottom aiming up the top of the tank had poor movement and had dead spots if they were aimed to high.

Next we might as well talk gph. Now I understand fish only and different types of coral need different amounts of flow and there lots of information about this online. What you can’t find online is there such thing as to much flow for certain coral? What about a tank with mixed coral types? That’s where pump placement and size of flow comes in I guess. Right now I have around 1400 gph total out of 2 powerheads with what I have in the tank should be more then enough for now. But my poor fish can’t seem to swim anywhere they school together and almost looks like there on a treadmill, is this normal? Fun to watch though.

Should the flow change? I’m guessing you don’t want the same flow day in and day out and I’ve seen the controllers that can turn your pumps on and off but does that really change the flow or just breaks it up?

What about at night I’ve seen some controllable power heads that have night sensors does this mean my flow should be slowed at night. Maybe put one of the power heads on the timer with the light? Or does it need to stop?

Now the reason I’m asking all of this is I’m looking at new power heads for my tank. I want something that will last and if I upgrade my tank size I can just switch tanks with them. At this time here is list of demands from new power heads.
Adjustable flow, want to be able to turn the gph up and down as needed
Controller friendly. Would actually prefer hard wired over wireless.
Small profile would be preferred with my tank size.
Depending on the responses I get my wants might change some. If night mode is ideal then that might be added
Is there anything else I need to consider before buying new heads?

Sorry so long winded and thanks for the help