You need to get your whole water system planned before you add more pieces that may not work together. You are on your way to spending a lot of money on something that won't work because you don't have enough water supply. Then someone will have you adding bits and pieces that they tell you will fix the problem, and before long you will have the plumbing equivalent of a crippled elephant.
First, decide how much water you need (gallons per minute for how many minutes) for your peak demands. Will a 7.5 GPM well meet those demands? Is the 7.5 GPM based on capacity of the well, or the capacity of the pump in the well? If the well will deliver the peak demand you would be much better off with a larger pump in the well than with tanks and booster pumps.
Even if the well will not deliver continuous demand, it may have the capacity to deliver the intermittent damand that you need for the new bathrooms with multi-showers.
Will the water heaters, apparently on separate circuits, meet the demands of their respective circuits?
A 1" PEX line will carry a lot more water than you can pump.
People have reported problems with the Davey booster pumps and they use metric parts that are hard to get. I would find something else.
The 3/8" feeds to the baths are probably too small for multiple shower heads, unless you will have one line to each head.
Do you have or need a water softener? The instant water heaters are intolerant of hard water.
There are so many questions that you need to answer for yourself before anyone can give you really good advice, but the first thing you need to do is decide how much water you need and the best way to get it.