The opposite. There's no need to read all of them. Each is self contained. So this amount just means you have a lot more to consume of you liked them

Not only is each self-contained, but I have found that each "sub-series"- if I can call them that- has a different vibe from the other, and are oftentimes entirely unrelated. So it's not like you're missing out on part of the story you were reading in Mort and Reaper Man by not reading a Rincewind book. Not many people actually read every book anyway.

Should be the opposite, there's a lot of options for where to start.

Just read Small Gods, which is fully self-contained and incidentally my favorite. If you like it, pick up another one and go from there. Most of the books are relatively short but all the ones I've read so far are amazing.