Through hull pick ups
 

How many do you have?
Where did you mount them?

I'm gonna end up with 4. 2 for the innercoolers and 2 for the engines. The innercooler PU's hang off the back on either side of the drain plug. Can I stack them inline to disrupt as little prop water as possible or will one pick up starve?

I've never seen 4 hanging off the back of the boat before. Is it common?
Is a straight 90 into the boat all that's required or should they be curved. At 100+MPH

You only need two. One for each engine, use ram horn style off of back of transom. make sure pickup is not behind props because can disrupt water to props. For inner-coolers use factory water line from outdrive. Use sand stainer for inner-coolers. sea strainers for engines. Make sure you use pressure gauge and pressure relief valves for engine cooling system.

When I do setups like this, I use the drive pick up for engines and intercoolers get it from transom pickups.

Do you have the option to use the drives for water ??

I've had the pick ups for the innercoolers in for years. The new drives are said to be too high and I won't get enough water for the shower and engine. I suppose I could try it first before I install all the extra plumbing but the strainers are soooo pretty.
I do have an innercoooler pressure gauge and relief. Also a water pressure gauge in the side of the block.

I have two PU's hanging off the transom now on either side of the drain plug. Would it be better to hang two more off the transom, which will be more likely to disrupt water to the props, or stick them straight through the bottom of the boat 2' forward of the transom, inline with my existing ones?
Is there math that could be done to show the disrupted water flow path. i.e. If I go through the hull, close to the keel, forward 2' from the transom, the path hits the prop, VS if I mounted them further forward and/or moved them 18" out from the keel the path would go outside the prop water.

Run the transom pick ups to the engines. If they are close to drain plugs they shouldn't interfere with the water prop. Unless the drives are out of the water you'll have plenty of flow for the intercoolers. I ran my 575's for years this way.