I see that you've put the red solo cups into practice with seed starting. Nice to see they have another use besides beer, LOL! I have discovered that the Smart Balance spread containers make excellent seed starting pots. I drill 6 holes, 1/4" in diameter, for drainage, & the seedlings do very well in them. Better even, than the green plastic pots from various nurseries. Maybe that's because the Smart Balance containers are predominately white? Dunno. But it' a cheap & easy method for me to use, with excellent results.
As for hardening off, yep, ya just can't put tender seedlings in direct sun, without frying them. If a good shade source isn't readily available, a shade cloth works very well, & they can be store bought, or home made. Another route I've taken in the past to protect young seedlings, is the use of old storm door, or storm window glass, painted with a 50-50 mixture of paint primer & water, or mineral spirits, depending on what type of primer you use.
They're free, & are made with tempered glass. Check your neighborhood on trash day. I use two, hinged at the top by drilling small holes thru their aluminum frames & zip ties to hold them together. This will form a nice A-frame. This is simple & I use this one, with no primer, for frost protection, if I need to keep a particular plant blooming for pollinating.
Here's the 1st one I made a few years ago. Not much on looks, but it did the job that year.
And what I now use, primarily for hardening off, I made from a greenhouse that was being scraped. I made two. Both have sliding doors, but one is open ended, while the other is enclosed. They are on a raised bed, using discarded carpeting, turned upside down, over stone dust (for drainage) as flooring. This is the enclosed one.
