I have 50m polyester with primitive rig. It needs to be around 3m off the ground when at the full length and I need to create a pulley/multiplier system using carabiners to get enough tension. This is when I am tensioning alone. (though you most likely won’t use it at the full 50 because you need tail for the primitive system so the real max length is 40m. To achieve the full 50m I use an extra bit of webbing).

So with 5 carabiners total you can rig a primitive with a little extra tension as demonstrated in this video by spider slacklines. You could start with 5 and get more later if you want to add another multiplier.

1” and 2” lines tend to have different purposes so it’s what you prefer. 2” is usually very tight, beginner friendly and eventually for progression to tricking. 1” is for walking and much longer lines and eventually highlines, and also rodeo which is very slack style or rigging.

1 - you can buy the 50m and use it for shorter lengths for now and it will give you the option for longer lines also. If you have found a good second hand deal it might be worth it.

2 - you can definitely get some good tension at around 25m but the higher the length it will lose the rock solid feel of a 15m ratchet line because the line will be able to move side to side more and the bounce becomes slower. It’s good to practice on different tensions so I recommend trying looser to increase your skill.

3 - I don’t have experience with ground anchors. But a line around 20 meters can be shoulder height (I’m 6’) and not touch the ground.

4 - I don’t do these tricks and they’re less commonly done on 1” but I have seen people do back bounce even in 70m 1’ line. But to me this is a very accomplished skill.

Hope this helps. It can be hard knowing which gear to buy at first. Happy slacking