How do a do a layout plan for my garden?

What a great space...lucky, lucky you!

If you plan on buying any plants or trees for this space, I would find out if there are any local nurseries that will do a free landscape plan for you.

If not, I would collect photos from all garden/yard designs I could and make your own layout...cut and paste your ideal yard and use that as a guide.

I'd consider hiring a landscape service/greenhouse grower that provides guidance for your grow zone, grading to assure rain will not flow in an unwanted direction ( towards your house! ) for for a project of this magnitude -- you have lots of big plans!

It doesn't have to be done all in one season.... start small and add to it every year -- or season - depending on your location. Stick with local growers, not 'big box stores' that simply want to sell plants!

There are lots of publications, and YOU TUBE productions that discuss yard re-makes ... BHG has great tools -- https://www.bhg.com/gardening/landscaping-projects/landscape-plans/

https://www.bhg.com/gardening/design/nature-lovers/welcome-to-plan-a-garden/

Can't design for you, but here's a few things to keep in mind:

1. what will grow well in the soil and sunlight conditions you have? If your plants are unhappy with either of these, they'll fail. Most state extension offices will do soil sample tests free, as well as have plant and growing recommendation.
2. how much maintenance do you want to do? Some beds are fine with next to zero maintenance groundcover. Some plants need careful feeding, watering, trimming/pruning and pest treatments
3. make sure you plant out your beds for the finished size of the plants. I know it will look sparse when first planted but when plants grow to size, you will have problems if too close together. Also consider heights of plants so the front of the bed's plants are not obscuring shorter plants.
4. some plants will be happier in different parts of the same yard even though it seems to us that the yard is all the same. You might consider initially putting plants in buried pots in your beds. Easy to move or replace as needed.
5. Overwatering kills more plants than almost anything else you can do, although overfertilizing can be just as bad. The difference is, you water regularly.
6. If using above ground containers, I recommend you stick to natural terracotta if possible. The sides are slightly porous and this helps the plant roots breath and water to be absorbed. Plastic does neither. If using plastic, avoid dark colored pots. In places where it is sunny, dark pots will absorb heat and you can actually cook your roots.
7. You don't need to use flowers as decoration. Consider doing at least part of the garden with a bed where you use colors and textures of non-flowering plants. You'll be amazed at how many different shades of green, and the sizes, textures and shapes of leaves that can be combined.
8. Do a websearch for outdoor plants poisonous to pets. The sites returned will typically include listings for humans as well. With both dogs and kids, you need to be careful. One quick example, Oleander, used in a lot of commercial landscaping is extremely toxic.
9. If you have an arboretum, or public gardens in your are, visit them for ideas in addition to nurseries. I have found that even in some of the "better" nurseries here where I live there is a mix of knowledge levels among the employees and some provided answers whether they knew the correct information or not. Plants are also not necessarily correctly labeled, even by commercial providers to the green houses. I have seen examples of where one particular variant of Basil was called by a different name by four different commercial growers and none of them were the correct botanical name even though they were all the same.
10. Not connected to the company at all but you might want to see if "Rich Earth" is available where you are. It is not fertilizer, but micro nutrients and trace elements from a fossilized dig site. I swear by it, and though skeptical as they come, a testing of one with / one without plants and using Rich Earth made a believer out of me.
11. 
    

Hope this helps and best of luck!

All good tips I see! I would take

a garden hose and lay it out, garden area, pool area etc. You can curve and shape any witch way. Leave it for a day or 2 then move around if you have a new vision. Spray paint your lines and get started, and go with some of these other great tips! Have fun :)

I don't know where you live, but here in MS & also in TN, the extension offices do charge for soil tests,but it might be worth it in the long run.