Welcome as well!
Ah, I was like you once. About two weeks ago. I had exactly the same problems and didn't want to resort to 'God mode' map updates.
This is the mod for you:
http://www.subsim.com/radioroom/showthread.php?t=147667
Troublous Haze pointed that in my direction. It's whole mod (plus a complete 20 min video tutorial) on manual targeting, where you gather range, aob, speed etc all from the scope. Also fixes the TDC so you can input the data and it will update properly. Sunk 200,000 (full realism) tonnes with that, with about a 50% hit rate - a very realistic mod. Well worth a look.
As for units, you're right in that the TDC is in 100s of metres (or hectometres). The KM used nautical miles for navigation, as nms are linked closely to knots (1nm/hr). Metres (and kilometers/hectometers) were used for ranging, attack, gunnery, depth and torpedo purposes.