X25X specs and sources have been kept private to avoid some gpu farms have an advantage at launch.
When is the transition to x25 and SIN planned?
What will need to get new SIN, having SUQA coins?
It will be announced pretty soon, probably next week. You need either 100k Suqa for a small SIN node, 500k for a medium SIN node or 1m for a large node.
Suqa will also be rebranded to SIN during the fork, my guess is about 2 weeks away if they announce it this comming week, but they will also release a testnet to help people set a node up.
They will also as you mentioned change the mining algorithm, a miner will be available but its a good idea to keep a close look at T-rex and such developers because they more than doubled the hashrate with optimizations for x22i