Okay.... I have been doing research for two days now and I'm researching myself in circles... some say you need CO2 some say you don't.... some say you can't use shop lights some say you can

.... so here are a few of my questions.... but first some background info.
I am a Planted tank (insert word that implies a noobie is a master). I usually kill plants terrestrial or otherwise within a few weeks. I've finally gotten terrestrial plants down now I want to try aquatic. I have some Hornwort three unidentified thriving plants in a RCS shrimp tank. I use Flourish on this tank a little bit 1-2 a week and I have a "plant bulb" "full spectrum" light in a shop thing over the tank. I bought a 2.5 gallon tank and put a regular aquarium light over it and they started to turn brown so I put another aquarium light over it.... so I put a shop light with a plant bulb in it and they've gotten green again. I upgraded the system to a 10 gallon tank with a sponge filter (for shrimpy baby protection TOO BAD ALL OF MINE ARE FEMALE DARNIT!!!) and it seems to have gotten better. The hornwort is taking over (Came with the shrimp). The largest unidentified plant (bought in a tube at Petsmart before I knew better in July) and it's doubled in size in the two to three weeks its been in there. The paragraph is chaotic which explains my RCS tank very well. I don't know the first thing about plants.... other than water... nutrients.... light... possibly CO2?
Questions:
1. What's the minimum size I should attempt as a newbie... I'm aiming for 2.5 gallons up to 20 as I'm working with a tight budget.
Any size tank will work for a planted tank. A friend off mine has a nice little 5 gallon hex that she breeds her cherry shrimp in.
2. What substrate should I use... I've found planting with sand is easier than gravel. Maybe a special plant substrate?
You can buy Flourite, which is an aquarium brand substrate. I, like you, work on a budget, so I just use regular top soil. About 2 inches, then cover it with pea gravel (which is another really inexpensive way to do it.)
3. What plants should I use as a newbie that's looking to not use CO2 injection systems? I would like a variety but I would like it to look balanced tall plants foreground plants and carpeting plants?
Different Hygros. I have a really nice one that grows very tall in low light. It has long strappy leaves. You can also use java ferns and moss, as well as amazon sword plants, and cryptocorynes (not sure if I spelled that right.)
4. What sort of lighting should I use... to simplify links to specific kits work well for me... I don't get the whole process of finding WPG and what not.
I just use the cheap clip on lights from Lowe's and put in a screw in Compact Florescent light in it. The squiggle bulbs.
5. I get that Hardscape is like rocks and driftwood... but I really have no idea how to do any of this.... can someone give me some pointers?
You can buy some cheap wood from Dr. Fosters and Smith. Large pieces of malaysian driftwood is like 13 bux.
6. Trimming? WHen should you trim how much and where? (as in stem... just leaves or whole plants...)
You trim when you feel the tank is getting over crowded, or you want to boost growth of your plants you have. YOu will want to trim the growing sprout and this will cause the plant to grow more stout, and bushier.
7. How do I make sense of what fertilizers and what not I need and how much of them...?
Flourish is a really easy fertilizer. I don't use fertilizers, just fish poop. Without CO2, there isn't as much of a demand for fertilizers, they kind of go hand in hand.
8. I want to do some fish and/ or shrimps. I want to do some Japonica shrimps some Otto's (if I get algae) and Killifish... COLORFUL killifish... any suggestions words of warning for this? I'd like to start with a 20 gallon tank...?
I'm not familiar with Japonica shrimp, but if you want to keep Cherry shrimp (very easy) I would keep them by themselves, with maybe otos. I don't believe the otos will eat the small ones/babies. Most shrimp won't breed if there is a lot of fish activity going on. However, I have two cory fry in my cherry shrimp tank, and they are still breeding. Shrimp tanks are pretty neat though, so don't think you would be missing out on anything.
9. FIltration? What type of filtration is good for planted tanks with fish in it (won't be heavily stocked)? HOB? Sponge? Definitely not UG.
I use a small HOB filter for all of mine, except the 10 gallon planted. It has a small Whisper internal filter, but not for any particular reason, I had it laying around, so that's what I'm using it for, instead of buying another filter.
10. Anything else that's absolutely necessary to know for a beginner?
Maybe join a local aquarium club, that's where I got most of my plants, for dirt cheap/next to nothing.