Updated question (adding more detail):

I am seeking advice on 1) any/all ideal root stocks to purchase fruit trees on and 2) the ideal shipping/planting months for my backyard (oct/nov or feb-april?). I intend to buy 1-3 year bare root trees and employ backyard orchard culture techniques to keep them 8-10 ft tall. I will plant 3-4 varieties or similar fruit types in one large hole, each spaced about 18” apart. I will plant a selection of varieties to ensure different ripening times throughout summer. The trees I will plant include a few varieties of each: apricot, cherry, peach, nectarine, and 2 asian pears (espaliered). I have very heavy clay soil with poor drainage. I will plant on a slight mound to improve drainage, drip irrigate, and cover with mulch. I prefer standard/semi-dwarf trees as opposed to dwarf since they are easier to source from nurseries and dont require support structures. The trees will sit on the south/southwest facing side of my property. My location is zip code 80016 and I range between zones 5a/5b.

Updated question (adding more detail):

I am seeking advice on 1) any/all ideal root stocks to purchase fruit trees on and 2) the ideal shipping/planting months for my backyard (oct/nov or feb-april?). I intend to buy 1-3 year bare root trees and employ backyard orchard culture techniques to keep them 8-10 ft tall. I will plant 3-4 varieties or similar fruit types in one large hole, each spaced about 18” apart. I will plant a selection of varieties to ensure different ripening times throughout summer. The trees I will plant include a few varieties of each: apricot, cherry, peach, nectarine, and 2 asian pears (espaliered). I have very heavy clay soil with poor drainage. I will plant on a slight mound to improve drainage, drip irrigate, and cover with mulch. I prefer standard/semi-dwarf trees as opposed to dwarf since they are easier to source from nurseries and dont require support structures. The trees will sit on the south/southwest facing side of my property. My location is zip code 80016 and I range between zones 5a/5b.

Thank you for your question. 

All fruit trees are grafted. The rootstock determines the mature size, disease resistance, soil tolerance, cold hardiness, and drought tolerance of the tree. For most home gardens, dwarf or semi-dwarf varieties are most suitable for ease of fruit picking, pruning, and management. It is best to purchase trees from reputable, local nurseries or mail order nurseries who can provide rootstock information. Bare-root trees (whips) can be shipped and planted in mid-April from online sources. Spring planting will allow the newly planted trees to have the time to grow an adequate root system to survive the first winter and beyond. Here is information on varieties that are recommended for Colorado:
https://cmg.extension.colostate.edu/wp-content/uploads/sites/59/2024/04/2024-Front-Range-Tree-List.pdf
Apple recommendations are on page 4, Apricot, Cherry, Peach, and Plum page 5, and Pear page 6.

General Fruit Tree information can be found here:
https://cmg.extension.colostate.edu/Gardennotes/771.pdf

Fruit trees need adequate spacing for growth and air circulation and you should plan on planting your trees so that they have adequate room for their mature height and width.  Even with pruning techniques and semi-dwarf tree varieties you should provide room for the trees to reach mature height and width. Height for semi-dwarf fruit trees top out at about 15ft and width about 4-10ft. 

Planting the trees correctly and with the proper depth is very important. They should be planted at ground level. Proper planting of new trees is covered in the following document:
https://cmg.extension.colostate.edu/Gardennotes/636.pdf
Care of newly planted trees:
https://cmg.extension.colostate.edu/Gardennotes/635.pdf

Pollination of fruit should be considered. Apricots, sour cherry, peach, nectarine, and European plum trees are self-pollinating. Apple, sweet cherry, pear, and Japanese plum trees are cross-pollinated. If growing one of these types, plant an additional fruit tree or an ornamental variety within 100 feet. For more information on pollination:
https://extension.colostate.edu/topic-areas/yard-garden/pollination-of-tree-fruits-7-002/?_gl=1

Fruit trees can have disease and pest issues, such as Fire Blight, Cystopora canker, and powdery mildew. There are varieties that have been bred for disease resistance. Insect pests include codling moth, Japanese beetles, and borers. Squirrels, rabbits, deer, and other wildlife can affect fruit production. Here is information on pest management:
https://extension.colostate.edu/topic-areas/yard-garden/backyard-orchard-apples-and-pears-2-800/?_gl=1
https://extension.colostate.edu/topic-areas/yard-garden/backyard-orchard-stone-fruits-2-804/?_gl=1

Pruning and training your fruit trees is another consideration. Proper pruning and training can ensure healthy trees and increased fruit production. Additional information can be found here:
https://extension.colostate.edu/topic-areas/yard-garden/training-and-pruning-fruit-trees-7-003/?_gl=1

Mulch around the trees can be beneficial for moisture retention. Do not put mulch up to the trunk of the tree, keep mulch 6" away from the trunk to discourage any burrowing animal such as voles. 

Many fruit trees need regular fertilization of nitrogen and other nutrients to continue tree growth and fruit production. Check annual shoot growth or do a soil test to determine proper fertilizer applications. Wrap young trees annually each winter to protect thin bark from sunscald. For more information on fertilization, see:
https://extension.colostate.edu/topic-areas/yard-garden/fertilizing-fruit-trees-7-612/

Going fruit on the Front Range can be challenging but when you are harvesting your apples or other fruit you will be glad you put in the work. Good luck!