Questions: rats, water needs, starting

Ok here it goes!  I am a complete newbie when it comes to permaculture so please be easy on me. I was told to ask questions to learn so here goes nothing.

I live in southern AZ and have a 40 acre parcel at about 5,600 feet.  Zone 8b.  I’m on a gentle south facing slope with a lot of caliche (ugh) and well draining gravel-y soil (if you are brave enough to call it soil).  The winter (Dec-Feb) gets down to about 15 degrees Fahrenheit, Spring is mostly windy and temperate and the summer is around 95 F most days in June with no rain before the monsoon hits in July- September with rain probably every 3rd day-ish.

There are a lot of ocotillo, senna, little leaf sumac, white thorn, mariola, banana yucca, nopales, pencil cholla, etc. on my land.

Hope this is a enough info to help me out!

Questions:
1.  This one is more of a moral quandary… how do you all feel about changing a landscape that is not natural for an area?  There is a lot of vegetation on my property that seems to be doing just fine but it doesn’t really provide much food for me.  I have heard that the vegetation that is here is mostly because of overgrazing in the early 1900s but should I be restoring it to grasslands or is it ok to work on growing trees and food producing plants?

2.  Rats.  Mice.  Big issue here.  We’ve tried planting a few things here and there but the rats rarely let them get more than an inch tall.  There are packrats, kangaroo mice and more.  How do you deal with this?  I’d rather not kill them… but do I have to if I want to grow a food forest?

3.  Water is an issue on my land.  No well, no city water.  We are planning to collect rainwater (we get 16-19 inches per year on average).  I’m trying to figure out how much water storage we will need in order to establish trees.  We plan to reuse all our grey water and build swales and basins but I don’t know what we need to get things started. Is there some type of calculation I can do to figure this out?

Ok!  That’s all for now!  I look forward to reading replies.  This stuff is exciting but also incredibly intimidating!

Kadin

Interesting topic!
I will admit I am not in a situation to add nuts and bolts value to your questions, but they did prompt some thoughts that might help you continue to frame your approach to your land.

First, when it comes to modifying a natural environment, I think you're on the right track when you recognize that what is the current "natural" environment may be more of current situation than a truly healthy natural environment. Digging into more of a historical land use perspective, studying how Indigenous inhabitants lived in that landscape, and understanding the implications of modern (last 150 years give or take) practices like heavy grazing, irrigation, etc and how they have modified your place into its current natural state will give you a more thoroughly constructed framework for your goals for your land.

This does lead a bit into the second thing that came to mind, which is whether your rodents are native or if you're dealing with introduced European rats (more recently modified natural landscape). I'm not coming down on a side when it comes to kill/no kill pest management or invasive/native, but I will approach harvesting an aggressive non native plant with a little less tender loving care than I will a possibly struggling native: I have no qualms about harvesting a whole patch of knotweed, but ramps or ginseng I will probably let be. Maybe similarly, rodents could be categorized for levels of targeted discouragement.

I'm sure you'll get a lot more practical responses but I thought I'd throw out some things that came to mind more in the mental framing side of things.

rats and mice are not a good thing anywhere. no only will they destroy your crops but potential for disease and parasites is high. get yourself a pride of outdoor cats and you will have loving pets and rid your property of menace rats and mice.

I second the suggestion of getting a cat.

We accidentally got a cat because her mother dropped her off and then ran off.

Our mice problem has ended.

I can't help with how much water you will need, because I feel it all depends.

My suggestion would be to harvest as much as you can.

Maybe start slowly in the first year with how many plants are planted.

As for water, I highly recommend looking at the work of Brad Lancaster:

https://permies.com/wiki/51855/Rainwater-Harvesting-Drylands-Brad-Lancaster

From the above link:

Thanks so far.

Do you find that your cat kills a lot of birds?  I have considered a cat but don’t want it to kill all the other wildlife. 😬

I have Brad Landcaster’s book.. great info and my main inspiration for even attempting this at all.

I’ve been watching the greening the desert videos on YouTube and considering starting with planting mesquite trees to have natural mulch and nitrogen to add to the soil as well as a shade provider.  Does anyone have experience starting their food forest with trees like mesquite?  I’m a bit concerned just because so many people consider mesquite an invasive that takes water from other plants…

I’m not big on cats but have always had barn cats.
They do great as long as you don’t feed them more than once a day, they tend to get lazy if you do.