The only thing you care about when talking about the range is battery capacity in Watt / Hours (WH). Sometimes on websites you will see Voltage (V) and Amp / Hours (AH), In the latter case you can calculate Wh as V x Ah. For example if your battery is 48V and 10AH you will get 48x10 = 480WH. This means that your batter is capable of supplying 480 watts of power for 1 hour or 24- Watts for 2 hour and so on. You can then use online bike calculator ( http://bikecalculator.com/) to estimate what power you need go with such and such speed with particular road grade, rider and bike weight etc. etc. Let's say it tells that you need 200 watts to go at 20 km/h. 480 / 200 = 2.4 hours. Cut it since there a losses down to let's say 2 hours. So 2 hours x 20kph = 40km.

You can buy ebikes with dual battery and you can always carry spare battery.

Hmm. What you're talking about there is a bit muddled. I get the upright riding with paniers. Awesome urban commuting or leisure trails sort of thing. Lots of bikes do that. And probably assumes a high proportion of teh power from teh battery and less teh rider. But that sort of riding will be at 20kph, and no-one really wants to be sat upright for 5 hours to do a 100km ride.

Alternatively there are the battery assist road bikes that are tarmac like (we have someone that rejoined the Saturday bunch rides post heart issue with a Specialised one, several other makes too. The specialised he uses for the 140km rides with 1500m+ climbing has a frame battery but then a plub in ancillary battery that goes into one of the frame bottle holders). And they are awesome for being a normal road bike but with that ability to add a bit of 'boost' power for hills or when the tempo goes up into a headwind (we sit him on front when it's strong headwind, then with a tailwind just drop him as the motor cuts out assist at 40kph ;-) )

But, those are different beasts, not sure there is a single crossover that's the 100kph ride friendly sit up and beg pannier lugger.

Oh, and $ is proportional to power * range. To get one that is going to have the power to go at a decent speed for a long time is really going to get $$$$. The sort of $ that make TT bikes good value.

My wife has the Specialized Creo. I believe the longest distance she has done on this ebike is 78 miles with 7000 ft of climbing. In order to do this, she had to order an extra battery extender. She has the bike’s internal system, another one attached in the back bottle cage area of the frame, and a third she puts in a bottle holder connected to the saddle (like you see on Tri bike set ups). On a much less hilly ride, she could complete a century with this same set up. Price for the bike, and additional battery extender, around $12,000 I believe

best ask on a motorcycle forum?

This is a weird question. Essentially the most inefficient setup that you can have (panniers, upright position) but then a battery to make up for it. I'm not sure I understand the use case. What do you need the panniers for? If it's a multi day trip then you'll have extra batteries anyway. If it's just 100 miles you have pockets and saddlebags, not sure what the panniers would be needed for.

It also depends on what the end goal of the ride is. Are you trying to keep up with a group, go further, go faster, or just make it up hills? For the first two a better (read: less upright) position will be more helpful. Knowing the use case would be helpful.

Thank you for the responses! Some of the requirements are strange, I agree.
I don't know much about e-bikes, but I think I got enough info to direct my friend in a right direction. Hopefully he'll have enough resources, I didn't know e-bikes are so expensive!!!