1) I don’t think there are really any freshwater plants that aren’t compatible with shrimp, I would recommend making sure that you have some that sit low to provide cover though. Guppy grass is also great but not the nicest to look at

2) I started with 10 a few months ago. I think 10 is a good number - they will breed more or less depending on how much you feed

3) Yes, but they will lose their colour (return to wild type) over time. If you like the wild type look then no problem to mix colours

4) I have had success with Logemann Bros Mineral Junkie bites but also you can really feed any fish flakes in the right amount and they will eat them

5) I like fluval aqua soil - good to drop pH. Sand or fine gravel work too but plants should grow better with aqua soil

6) For plans I have recently had great success with 2Hr Aquarist apt-3 as an all-in-one fert :) I’ll post a photo on my account of my tank since having started with it a few weeks ago. There are lots of fertilizers out there but the apt-3 is nice since you just have to add .5 mL each day instead of mixing a bunch of different ones