Compared to 5.0, biomes are bigger in the 5.1 beta version.

Possibly, it would make sense to leave the terrain unchanged, to not reduce the size of mountains too much, and only adjust climate parameters that only control biomes.

If you want to work on this though, follow your own intuition, and experiment how smaller terrain would feel like. This probably needs some iterations anyway and there is no "wrong" approach, anything is useful for getting feedback on.

Worldgen is a bit more complex. This Discord is an amazing place to get help tho if you are new but interested in learning some worldgen stuff: https://discord.gg/qYvzwNFcsx