In order to follow the 1/2 veggies and 1/2 liquid guideline, should I
use a measuring cup to measure out the cut up veggies before adding
them to the measured liquid?

The half and half guideline refers to filling the jars not making the mix itself so as long as you have enough liquid to insure each filled jar is only 1/2 solids you can add whatever amounts of each you prefer. It is an eyeballed 1/2 and 1/2in the jars not necessarily a measured 1/2 and 1/2. Slotted spoon to strain out the veggies and into the jar until 1/2 full, then fill it the rest of the way with the liquid, ok?

I assume I shouldn't really cook the soup much before processing, since
it will be pressure canned for 75 minutes. Otherwise, the veggies may
get way too cooked down?

How long you cook all depends on the vegetables you use. Instructions say to cook each vegetable as called for in its own hot pack instructions so assuming no meat, no meat broth, or beans is included you'd look up the hot pack cooking times for each of your vegetables (or nearest equivalent) and then cook the soup for the longest of those times before filling the jars. For example carrots is 5 mins., kale and cabbage (spinach) is 3-5 mins., etc. Just off the top of my head (so double check your vegetables) I think most on your list would fall into the 5-8 mins. range. If you use other vegetables or meat or meat broth or beans then longer time is required.

Dave

PS: and no pastas even if it is a Minestrone.

Thanks Dave, this is going to be way too easy :)