Sounds like a plan! Consider a min-max thermometer and a light meter to take readings very so often. That way you can set up some parameters for you buying. You'll also know the spots on your porch that get more/less sun or are hotter/hottest
and you will be ready to place your new orchids in the optimum locations for their continued happiness.
Once you purchase, watch your plants carefully. Too much sun is typically evidenced by a reddish hue on the leaves. Although the color won't go away, you want to get them out of the sun as soon as/if you notice it, so that there isn't worse damage.
lastly, be sure to post pictures of what you buy and let us share in your success!