Hi,
1. Save data is locally stored in your device. So uninstall the game would clear your save data.
You can transfer for data to a new android device when you move all datafrom your old phone to the new (using such app like Smart Switch by Samsung).
Login using Itch-io will restore access to the game, DLCs but not game progression.
We'll continue to improve this sytem in the future. Right now, we're focusing on deliver contents first.
2. Right now it's about 3~400 MBs. But we suggest to have ~800MBs available to save spaces for future updates. We have further optimized the game in this Remastered to be as light as possible while packing huge amount of artworks.