1- How do you see if there are new replies posted in the threads you have posted. apart from subscribing e-mail notifications and advance search? or how do you see all the threads you have posted?
Easiest way is to refer to the Envelope icons to the left of each thread in the Forum view. There is a key at the bottom of the page. You can easily see which threads you have posted in (arrow).
2- how do you subscribe to a thread without posting in it?
Use the drop-down Thread Tools menu (Subscribe) in the yellow menu at the top of the opened thread.
You might also want to experiment with the different Display Modes on the same menu bar. There is an FAQ on the topmost Forum Menu Bar that explains them.
SD