I prefer morning sun and afternoon shade when I consider an area for planting. If you figure here we get about 13+hrs of good sun per day and afternoon is the hottest time of the day you want to plant an area that starts getting shaded an hour or so after noon. My second choice would be an area that gets sun mid morning and shade mid afternoon followed by an area that gets sun after noon till dusk. That said I am planning for at least 6 hours of full sun by simply noting when the sun hits an area and the shade covers it fully (or mostly) blocking the sun. In a forested area you will find patches that get full sun at various times and for example if an area gets full sun in the morning for 3hrs and then afternoon for 3 hrs it does not mean it is getting a full 6hrs straight. What most people do not realize is plants have a daytime and a nighttime mode. The 6+hrs of sun is needed for photosynthesis (or the daytime mode of plants) it should be 6hrs straight. Now you can grow things given less than 6hrs sun and can even break it up into smaller patches totaling 6hrs but they will not grow as well as getting at least 6hrs of full sun.
If an area grows grass well it is suitable for veggies is a good general assumption in regards to does the area receive enough light. Now grass can tolerate a full day's worth of sun as well as higher temps than veggies like/need. Using grass growing as a judge to whether crops will grow has to be combined with the fact grass will grow where veggies will struggle.
As far as clearing your land it sounds good however is it going to be a square, rectangle, oval, circle, if a rectangle situated n/s or e/w there are a lot of things that need to be considered and only you can judge if what you have cleared provides enough light for your crops. I do however recommend clearing based on the side of not enough rather than too much because it is a simple matter to cut down the tree (or trees) shading the veggies but impossible to replace a tree you cut down without years of growing.
The open strip might make a great place for a garden or you could clear for plants that would prefer some shade as well as sun and plant the strip will sun loving or tolerant plants. I have not seen the strip to know for sure. One thing though why is the strip there in the first place? Is it a clear cut for say power lines, firebreak, just simple an area where trees have not taken back over (IE once was a pioneer's garden), or naturally tree (or even other plant) barren area due to unknown reasons? Lots of stuff to consider when looking at using a natural (or unnatural) clearing in an otherwise wooded area.
I too get jealous when I see others with a wonderful garden especially when my first couple of years were flops including some expensive trees that simply died or got
root bound and had to be replanted. That said I have a much different problem than you as I am dealing with a lot of fill and clay trucked in as well as dug out the ponds in the area. It seems everyone with a
pond had it dug by the guy who cleared and built on my property ("Hey I'll dig you a
pond if I can keep the dirt"). He basically filled in a low lying area before he built. Over the years though I have been able to bring small areas back to life and finally this year think I have a decent garden plot and have started to see trees thrive. It took a lot of trial and error as well as hard work to get to this point and will take a lot more to get to where I want to be. That in itself is part of land ownership and management doing things that make it better for the long haul. You may not see results your first (or first few) years but if you are doing things right eventually you will see results and it will get better and better over the one resource we cannot take for granted which is time.
