Mt. Aso

We are taking our first trip to Japan April 19-May 3, and we would like to visit Mt Aso, Yufuin and Beppu (if Beppu is worth seeing) as part of our trip, but I got the following response from a tour planning agency regarding Mt. Aso:

we generally do not recommend travel to Mt. Aso for independent travelers who do not speak fluent Japanese or are not accompanied by a full-time guide. The area is rather remote and the only way to get there is by private car. We have occasionally made arrangements for a half day car to Mt Aso, then on to Kurokawa Onsen, however, at that time of year the proprietors of the ryokans are swamped with Japanese guests and would not be predisposed to take guests with whom it would be difficult to communicate.

I'm not sure what to make out of that response after reading about the bus schedules from other comments/questions in the forum. Is it necessary to have a guide or could we be happy to explore Mt Aso on our own? Basically, we wanted to visit a volcano during our trip and Kyushu sounded very interesting, but if you have other recommendations, I'm open to suggestions.

Other cities we will visit include Tokyo and Kyoto which I was hoping would coincide with the cherry blossoms for our dates. Are these dates too late (April 19-May 3) and any recommendatios on where to start?

Sorry for the long winded message and thank you for your help!

The area is rather remote and the only way to get there is by private car.

It is simply not true that a private car is the only way to get there. And even if it were the only way, you could still rent a car!

Here are the facts:

There is a train between Kumamoto, Aso (need to take a local bus from the station to the mountain peak), Yufuin and Beppu. Furthermore, there is a bus between Kumamoto, Aso (some go directly to the mountain peak), Kurokawa, Yufuin and Beppu. The trains are easy to use even for people who do not speak Japanese, while taking the bus might be a little bit more challenging, but should also be doable:
http://www.japan-guide.com/e/e4552.html

And as mentioned before, the area is a great place to be explored by rental car. It is probably the easiest way to get around:
http://www.japan-guide.com/e/e2024.html

Are these dates too late (April 19-May 3)

Yes, in most years, this is a little bit too late for "mainstream" cherry blossoms in Tokyo and Kyoto. During late blooming years, you might still see some blossoms around April 19:
http://www.japan-guide.com/e/e2011_when.html

I managed to reach Mt. Aso via train and bus, though it was a few years ago. It shouldn't be a problem. English is taught extensively in public schools here in Japan. Patience, some Japanese phrases and a good map, can get you far.

If you can't manage Mt. Aso, consider Sakura-jima near Kagoshima. It is stunning if you have never seen an active volcano. The nearby volcanic, beach-sand baths in Ibusuki are also a great experience. The overly touristy "hells" (jigoku) of Beppu are a "love it or hate it" experience, but the onsen (public baths) and ryokan can range from pleasant to luxurious and the main attraction. Also, consider Kumamoto if you have the time.