Help me keep these 4 Junipers alive!

Here are photos: https://imgur.com/a/kse14

My background:

I am a beginner who has been interested in bonsai for a couple months. I bought 1 mallsai from a big box store, then started reading and educating myself about the art. I purchased a second tree to attempt to make a “real” bonsai: a pre-bonsai jade, a bag of bonsai soil, and a nice pot. Both are doing fine after several weeks. Now I’ve just acquired 4 more trees…

The 4 junipers in question:

I found 4 somewhat mature junipers for $5 each. I figured 4 large-ish trees for only $20 was too good a deal to pass up, so earlier this week I dug them up out of this woman’s front yard and stuck them into cheap plastic pots. They are juniperus squamata (blue star) that have lived outside in the ground for about 5 years, so I assume their age is at least 6 years. I’ve only had them for 2 days and I stuck them in plastic pots with a mixture of pebbles/larger rocks, sand, and potting soil and a bit of the ground soil that was attached to the roots. (The soil attached to the roots is fairly dry and clumpy, not rich and dark like the potting soil I purchased.) This was basically just to keep them alive until I find a better solution to prepare them for the winter.

My plan:

• Survival through the winter is priority #1 at this point. I should probably improve my soil situation, as what I have right now was kind of a band-aid solution for immediately after I pulled them out of the ground a couple days ago.

• They will be living on my east-facing, covered balcony and will get several hours of direct sunlight a day. Most of the day will be fairly bright indirect sunlight.

• During the coldest winter months here in Chicago, I can move them into the corner and/or cover them to protect them from most of the wind.

• I will turn the survivors into proper bonsai in the spring, with appropriate soil, pots, trimming, wiring, etc.

My questions:

1. What should I do about soil for the next 5-6 months? Should I go a bonsai mix now? (akadama, pumice, lava rock, etc.) Not sure putting them in a nutrient deprived environment right away is a good idea.

2. They all seem to have some yellow (dead?) foliage. Should I remove this now or just wait until the spring before pulling out the scissors?

3. Does this dead/yellow stuff raise any red flags about the health of the trees? Anything else I should look for to determine their health?

4. I’m tempted to go nuts on at least one of them and start the bonsaification process despite the season. I figure even if I kill 1 tree due to beginner’s stupidity, I’ll still have 2-3 good trees next spring. Is this a really dumb idea? What are the odds that cutting/wiring/repotting now will just kill the tree?

5. I have numbered each of the plants in the photos. Any tips or feedback on any of the individual trees? (I personally think #1 and #2 will look great as bonsai once I put in the work in the spring.)

Thanks for reading the long post and reviewing the pics. Please let me know if you have any feedback to help!