How to tell when you need to sharpen?

This video will let you know what your options are for a refresh.

Straight Razor Honing-Refreshing Straight Razors - YouTube

Good luck

Get a barbers hone from ebay. Inexpensive and they work. 4-6 laps, a good stropping and you are back in business.

DAHE4, where's home when you're not in Japan? Put in your location and maybe someone nearby will chime in to help.

+1 to the suggestion of a second "reference razor." I didn't know how sharp they should be, or how good they should feel, until I bought a professionally honed blade.

Best wishes to you.

I'd go ahead and give it a quick rub on the Norton 8K. There's a rabbit hole of information on using the Norton 4K/8K on the forum.

The Bengall is likely a decent bit of old Sheffield steel, here's a few others:
http://straightrazorpalace.com/razor...-brothers.html