I plan to buy Minecraft and the 2 editions are suggested to me. I've read through the descriptions for it too, but it doesn't say anything about gameplay per se. And before I search the internet, I want to hear someone else's opinion.
Is there a difference in gameplay between Java and Windows? And can you install mods on both versions?
I have both versions and have a lot of experience with them. I've been playing Java since version 1.8.8 and Windows 10 for at least 2 years
Java advantages:
Mods
free resourcepacks
good and free adventure maps
Disadvantage:
Runs very unnecessarily! Java is not recommended if you have a medium sized laptop
Java lags sometimes (no matter which PC)
Windows 10 edition advantages:
Runs much smoother than java!
almost no lags
you can play at a very high render distance.
When you are in a world friends can just join if you want
Disadvantage:
No mods
You can only have free resource packs if you convert it with a converter (Java resource pack to Bedrock)
Opinion: Windows 10 runs really great! But if you want to play with mods Java is better, but you need a good pc
It is also important which version you like. Because there are many different features and mechanics (Redstone is very different!)
With the Windows 10 version you can pay for things but you don't have to!
Java doesn't necessarily have the better servers, I think it's good on both versions.
And Java is in need of performance
With the windoof edition you have to pay for many addons and texture packs (at least that's how it was when I looked at a friend who plays on the bedrock edition) and with Java you usually never have to pay. Still, Java has the better servers. See Wynncraft as an example. Java requires performance, that's true, but you can get a lot out of it if you play with Optifine or similar modifications.
I have a pretty bad laptop myself, and even there I can play the Java edition smoothly with a medium render distance.