For the XYZ panning use the sliders or enter the exact value. Use the mouse for rotating and zooming.

An addon would only complicate the usage (although we are working on it). You will be working with nodes just like you're used to.

Terrain Mixer GN (Geometry Nodes) supports Eevee and Cycles. In the original Terrain Mixer, when you're done with setting up your terrain (with Cycles nodes) you can easily bake the maps (Height and Diffuse) and use them in Eevee.

Once you get used to it - yes. With the Image Mask node, you can get pretty accurate when adding lowlands. Also, you can rotate maps individually which gives you a lot of power.

2000x2000 meters. Try not to change its size while working with the material nodes. You can do anything you want after you bake the heightmap and apply it to a new plane.

Actually, you can make new ones by baking the results of your mixing. If you want to invest in a more professional tool for generating terrains and heightmaps, try Quadspinner 'Gaea'. That's the tool we use

After you define the shape of your terrain, bake the heightmap and apply it to a new 'Plane' object with the 'Displacement Modifier'. After that, you can play with particles.

Terrain Mixer for Blender allows you to choose between 'Cycles' and 'Geometry Nodes' workflow to be able to generate realistic and abstract terrains with almost no effort. The workflow is SUPER-FAST!