23.5" will likely be too small for you at 6'5". I ride a 23" at 5'11".
Here's a basic place for you to start with sizing and how to measure a C&V frame:
https://www.vintagevelo.co.uk/frame-size-guide/
My very baseline for what qualifies as a worthy purchase. There are exceptions to all of these rules, but they are good rules of thumb to start with:
- Chromoly frame
- Downtube shifters instead of stem shifters (not because stem shifters don't work well, but are typically relegated to lower end bicycles)
- Rear derailleur hanger built into the frame (for the same reason as stem shifters)
- Alloy wheels rather than steel
Nice to haves for a commuter:
- Room for fenders if you're in a wet environment and might want them (Boston can be quite wet)
- Decent attachment points for said fenders as well as a rack