LOL! You don't want a street bike? What do you think a Harley is, a dirt bike? 8^)
A Honda Shadow is a good place to start. 750cc, about 45 or 50 hp (I could be wrong). Harley is making a new 'Street 750' and 'Street 500' which are very similar to a Shadow, which might be perfect except you shouldn't (IMO) learn to ride on a brand new bike. The Shadow's been around forever so you could get a very nice used one fairly cheap.
Or a Kawasaki Vulcan 800 or 1100, or a Suzuki C50 or M50, or I think Yamaha Star has something in the 800-900 size range.
This size, between 750 and 100cc, would be too big to start on a standard bike but cruisers have a very low center of gravity so the bike feels much lighter than it actually is. Plus bigger ones are not necessarily faster, the size is for stability and stamina on the highway.
A Sportster would be okay too, after all, that was Harley's 'entry level' bike for several decades before the Street 750 and 500 bikes came out this year. I think it's kind of a clunky bike, but they are VERY popular, especially with beginners, so WTF do I know? 8^P In comparison reviews the Sportster always comes off as the slowest, clunkiest, least comfortable bike in the class. (Look on YouTube for 'cruiser comparison test', 'cruiser shootout', etc.)
Cruisers are relatively easy to ride and also relatively safe, because they support a relaxed, laid-back riding style. A cruiser would be good to learn on even if you wanted to graduate to a sport bike!
The power isn't the problem, it is the weight. The bikes Smarty is looking at are 500 pounds.
Lighter is easier to ride. Some of us never want overweight bloated bikes.
There is the Honda Rebel 250, Suzuki GZ250, and the Yamaha Virago/V-Star 250 -- all about 330 pounds, all capable of 75+ mph. I ride a Vespa 150 on the freeways of Los Angeles. A 250 *IS* acceptable on the highway. But if you need more speed, a 85+mph Suzuki LS650 Savage/S40 is a 380 pound 652cc single cylinder cruiser.
If you don't need freeway speeds, you can get smaller and easier to ride bikes, the new Grom, a SYM Wolf 150, or a SYM Symba 101....
If you have the money there are Harley Sportsters. They're lighter, with smaller engines, Harleys aren't cheap though, there are defiantly some cheaper 234cc Hondas.
ducati 696
Practise a lot
