The Pro-107 will not suit your needs for digital scanner as it only does analog voice. It will only be able to hear just about what your UV-82 can hear now, but will probably be able to scan those frequencies faster. It might also give you some coverage on trunked radio systems that are analog (anything that operates Mode "A" in the trunked system). If you want to listen to anything on MARCS, you will need at least a P25 Phase I scanner, but it also wouldn't hurt to consider a P25 Phase II scanner as it is backwards compatible and in the event MARCS switches over to Phase II. Here's a list of the portable battery powered digital scanners on the market right now.
Current Model P25 Phase II Scanners:
Uniden BCD436HP (Handheld)
Current Model P25 Phase I Scanners:
Uniden BCD396XT (Handheld)
Special Case P25 Phase II Scanners:
The following model is discontinued but may still be found online. Will eventually be resold under a different name in the future.
GRE PSR-800 [Future Whistler WS1080] (Handheld)
Special Case P25 Phase I Scanners:
The following model is discontinued but may still be found in local RadioShack stores and online. Will eventually be resold under a different name in the future.
RadioShack Pro-106 [Future RadioShack Pro-651 & Whistler WS1040] (Handheld)
Discontinued P25 Phase I Scanners:
GRE PSR-500 (Handheld)
RadioShack Pro-18 (Handheld)
Uniden BCD396T (Handheld)
Older Discontinued P25 Phase I Scanners (Lacking 700 MHz):
RadioShack Pro-96 (Handheld)
Uniden BC296D (Handheld)
You do not need the CTCSS tone to receive transmissions on a frequency, but a CTCSS tone may help eliminate interference that you might get on a frequency. If you don't get any interference on a frequency without CTCSS then it really optional if you want to put in the CTCSS.
A lot of people seem to find them at pawn shops, thrift stores, or just online where people just want to get rid of their scanner for a little bit of cash.