I saw already done reviews in the game so I would just give 2 advices in the beginning:
Always answer an approach move on a 4-4 (F16=>D14) A double attack is sometimes manageable but it’s hot and heavy duty. Avoid it.
The S18 move is a urgent move because it’s life for both and a mountain of points. Urgent moves come before big moves.
No at this stage you can just fish a few points in the endgame but you can’t save the 5 stones. The thing is it’s just 5 stones… Consider instead a move at D9 for example.