Help with some big ol' used DIY speakers

A good friend of mine, passionate about music but new to this hobby, is putting together a system on a dime, a nickel if he can help it. It's a fun project. He recently picked up a pair of whopper DIY, homemade speakers for free (craigslist). He rolled them into his office and this awesome picture tells the story:

https://imgur.com/z2lAvpy

Two questions. First: is there any way to look at those speakers and gauge the kind of amplification they'll need? The guy who built the speakers implied they were rated at 8 ohms and were quite efficient. He said he was using an old 90 watt receiver, and said that even 40-50 watts would be fine. (We're not talking class A here.) I don't think he knows the other specs, such as sensitivity, etc. Maybe it's because I have mini monitors that are underpowered at 200 Bryston watts, but I can't imagine driving those big boys for a house or lawn party with an old 50 watt receiver. I'm hoping my friend can try out a few different amps but that may not be possible. The question is: is there any way to look at those and guesstimate what he needs to drive them? Or, without knowing their sensitivity, is it really just trial and error? Keep in mind the ethos here: free or close to it. So while you can never have too much power, it's also much easier to find inexpensive used receivers or integrated amps at 50-100 watts. (Of course, the watts rating of a receiver or amp doesn't really tell us all that much, but it's likely the best guide as my friend looks around at used equipment.)

The second question is about the wiring. The speakers are in two cabinets, with the woofers below and the tweeters/midrange above. The man who made them simply runs speaker wire from the amp (receiver) to the base cabinet and then more wire from the terminals on the base cabinet to the terminals on the top cabinet. That makes sense, I guess, but without crossovers I assume that the full-range signal would be going to all the drivers. This might not be ideal for the quiet moments of a Chopin etude, but as long as the timing sounds okay, are there any issues with this? I've never done this kind of thing before. I can't imagine my friend would want to plunk down money for an outboard crossover, if that would even work, but maybe. Thoughts?

As you can tell, the goal here is to have some fun putting together a system for as little money as possible ... and to have all kinds of fun cranking tunes and throwing parties!