1. Radio tower counts as an icon on the map yep!
2. You can use the same tower to decrypt all maps. Since that tile is a place you've visited before you would do steps (A-C-H-F-G) the event for the radio tower building would be decrypting the maps. So once you've done those yes, your day would end. (You can do all 3 in the same day)
3. Tiles with a treasure icon on them work like I demonstrated above. A-C-H-F-G. The 'event' is just finding the treasure no exciting text for those im afraid. The decrypted maps should tell you the terrain of the area you unlocked. Basically grab treasure and end the day.
if it lands on a tile you've been to before, you'll use the priority map to find the next possible spot. Just go up the numbers. (So if you rolled a 12 and it's not a mountain like map 8 wants, you'll check tile 13, then 14 and onward until you find a blank tile or the terrain that the map points out. ) it's like the map says "this treasure is somewhere south in the mountains", use the compass to find it.
ts8 has you throw your weapon, so you can't use it again next turn if you only have one weapon left! You can only throw a weapon once per battle. I would save that for the end of battle.
The last cryptic puzzle is very hard! But I bet EVEN you can figure it out, especially since you got the maps figured out.