Converting this site to a productive home orchard is a longer-term project than you expect. Recovering compacted clay soil to allow a healthy home orchard will take time, and soils are already too cold and daylight too short now, in late October, to expect good luck starting a cover crop. (WSU cover crops publication)
I'll share some helpful publications, and then ask if we have an expert available to provide step-by-step recommendations for you. If you do not get an additional reply using this web forum, contact the Metro Master Gardener Volunteers directly.
"Soil: The Dirty Secret of a Living Landscape Soil", EM 9304, is a good start on understanding soils. "Improving Soils with Organic Matter", EC 1561 is also helpful. Don't walk on or work the soil once it gets wet without advice to do so, as it makes compaction problems worse. Another key concept is to understand that water and roots do not easily cross sharp textural differences in soil, so layering on topsoil might not be advised. Soil testing will be useful at some point, but I'm not sure when you should pay for that, given the difficulties of your site.
This page, "Home Orchard Concepts", lists publications from OSU Extension about orchard considerations when choosing, planting, and caring for trees.
I expect you'll hear more from us within a few days.

Soil disturbances change physical, chemical, and/or biological properties. For example, soil pH may be high or low relative to that tolerated by plants, soil fauna, or microorganisms. Salt contaminants may increase soil electrical conductivity. Physical mixing of horizons may occur when placing a cement platform, changing water and nutrient holding capacity. Use of heavy equipment can compact soils, increasing soil bulk density and penetration resistance, and reducing infiltration and percolation rates. Many of these changes can have serious impacts on plant rooting and microbial community function.
Soil testing is an important first step toward growing healthy plants in your garden. A soil test can help you:

Make informed fertilizer and soil amendment choices.

Diagnose and correct plant problems.

Learn about a new garden or growing area.

Enhance plant growth.

A pH test will tell you how acidic or basic your soil is. Most plants prefer neutral soils, but some plants grow best in more acidic soils (blueberries, rhododendrons, azaleas, etc.). Soil nutrients are also affected by the soil pH.

Here is an excellent soil testing service:
ALS Environmental
1317 South 13th Avenue
Kelso, WA 98626
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Web: http://www.alsglobal.com
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Here are some important publications to review:

https://catalog.extension.oregonstate.edu/em8677/htm

https://extension.oregonstate.edu/gardening/soil-compost/how-do-i-test-my-garden-soil