try kingbrightusa.com too, example
1-Digit 4.0in LED from Kingbright USA
Or make your own digits, chunks of LED strip lights for each segment.
The digikey/mouser parts are faint, only 10s of mCD. You need much more for outdoor use:
These will show up nice!
Yes, Arduino pretty easy to use. Programming seems like fancy BASIC to me. But then again, I've been exposed to a lot of different software over the years. Biggest challenge to the coding was keeping the ; and { } straight when I started with Arduino. Gets easier the more you do it.