I've done plenty of cycling...Hope to commute at least twice a week by bike weather permitting... The Kathmandu has a "rack time" rack so I'm really choosing between a pannier or rack bag above the rack, for stuff I need to take to work.
Ok.
Well I'll chuck in my experience as I often use a Cube Reaction hybrid to commute to work and that's 25 miles one way.
2 or 3 times a week (with a gap between the days) is probably a good target. Even though its an ebike, unless I'm really in shape and doing it super regularly, my body often can't handle consecutive 50 mile days! yes I must be a lightweight. Its often not my legs though, its also my shoulders, neck and arse that get sore! YMMV though, but being a normal human and not a TDF rider (or a spring chicken) I struggle at that daily mileage.
I absolutely love my Topeak Trunk Bag DXP With Velcro Mounting Straps. This probably will fit on your rack (maybe - check) although it will not use the rack time system - just velcro on.
Appears to be in stock (often isn't!), I'd order one ASAP
https://www.tredz.co.uk/.Topeak-Trunk-Bag-DXP-With-Velcro-Mounting-Straps_55311.htm
Those pictures don't really do it justice. Its just a nice looking, quality rear bag in normal use (where there is plenty of room for say a charger, some small change of clothes etc), but the ability to unzip the sides to have fold out panniers is a often a godsend for extra clothes etc. I often go shopping on my bike and its surprising how much you can fit in with this particular Topeak model.
I've tried cheaper crap from Amazon etc, but the Topeak stuff is in a different league.
With a 625wh battery, if your ride is flatish, then you could probably get away with not needing to charge in work if you ride in tour or sport. I'd take the charger in with you a couple of times though and see how you go.
Where I live, its hilly, and I live on the elevated end! so with my 500wh battery, I can make it into work using only 2 or 3 bars (out of 5), however coming home in turbo (as I'm usually knackered then at the end of the work day), I'm almost totally out of a fully recharged battery by the time I get home (because of the elevation gain returning) so I HAVE to keep a spare charger in work and totally recharge when I'm there.
I've become fairly good at planning ahead, so what I do is when I take the car into work, I take clean clothes, towel, food etc and stick them in a locker. Then when I cycle in, I don't have to carry all of that on the bike (even though I could if I wanted to).
If its hot and I push it (or if I ride in on a non electric bike), then yes, I certainly have to shower.
On cooler days and I'm in turbo, then I can usually get away with not showering if I don't want to
If you're doing those sort of distances, use proper cycling clothing - technical gear with good comfort and wicking ability etc.
Lights and winter/wet gear is for another conversation. I'll stop there for now.