1. MPGSK isn't meant for mobiles. It uses Unity's terrain, which isn't optimized for mobile platforms. It also has no controls for mobiles at all.
2. Same random seed means same generated data.
3. Probably, yes. It's better to generate the terrain at edit time instead, and turn off the generation script. This way your terrain will be saved.
4. Yes. The same parameter that adds mountains around the side. Reverse it and it will instead create an island.
5. I currently don't have any plans for this. The next game I'll be working on targets desktop computers rather than mobiles, and I don't make features that I don't use. That's how I keep the quality bar higher than I could otherwise.