Welcome to the sport! I’ve been riding a year myself.
I looked to rent as well, and found no options available whatsoever outside of the aforementioned Harley $150 per day route. It sounds like the deal you have found is great - use it to experiment with as many bikes as possible. While I didn’t rent, I had a good friend who loaned me his BMW F650, and the experience was invaluable. I mostly learned what would *not * work for me.
If you’re as new to motorbikes as I was, you probably don’t know about the difference between bikes with low-end torque vs high end torque bikes. The high end torque bikes are usually sportbikes and the like - they’re made to perform best at high speeds, which means they’re pretty finicky when you’re going slow. My Buddy’s F650 isn’t a sportbike by any means, but it was finicky enough to keep quitting when I tried to accelerate from a dead stop, which was really embarassing at intersections where the light had just turned green. This influenced me to look for an incredibly forgiving bike when it came to torque.
(This torque business also has a lot to do with the way a bike is judged, BTW. A 650cc sportbike performs a lot different than a 650cc cruiser. When veterans advise you to buy a bike with fewer cc’s as your first bike, they’re primarily worried about you getting a sportbike. I read somewhere that the average lifespan of a new motorcyclist whose first ride is a sportbike with 1000 cc’s or greater is less than a year. Choose wisely and ride smart!)
Another factor for me was the physical size of the bike. I’m 6’7’’, and I simply wasn’t comfortable on most bikes. In fact, I’d say it was downright dangerous - I’d have to fold up my legs fairly tight to keep my feet on the pegs, and I wouldn’t have enough free movement to reach the rear brake in any kind of natural fashion. Even worse, the F650 has indentations for your legs to go in, and my legs wouldn’t fit into them. Bike salesman were awful - they kept telling me I’d get used to it, or would encourage me to buy a bike and add extensions, with no gaurentee it would work. My experience with the F650 demonstrated to me it was bad enough not to “get used to it”. I bought a bike that fit me off the lot. (One of the very few that did without costing a fortune, in fact.) Don’t listen to anybody tell you you’ll “get used” to a bike if it’s uncomfortable. Although it’s rarely mentioned in the literature, the ability to comfortably access all the controls of the bike and see the mirrors is absolutely the most important feature. Since you’ve mentioned that you’re heavyset, I’d add that you need to experiment with how the bike corners. I require a low bike, otherwise the center of balance is too high.
So my advice is, try as many as possible, don’t get too attached to the idea of ending up with the Shadow because you may find you’re more comfortable on something else. (You’ll probably still end up getting the Shadow - it’s pretty standard. But still, keep your options open.)
Unsolicited advice: get a copy of Proficient Motorcycling by David Hough. Simply put, the best book out there for riding safely. Hough explains road dangers you’ve never thought of. (In fact, the MSF course is mostly based on his book.) Another good one (recommended on one of the better motorcycle boards out there) is the Idiot’s Guide to Motorcycles. Jay Leno’s introduction had some of the best advice I’ve read anywhere. The safety section of the book is essentially a restatement of Proficient Motorcycling (but not as good.) The best part of this book is how it explains the history of Motorcycles, the different types of bikes and engines out there, and some other details. It’s because of this book that I can maintain a conversation with most motorcycle guys.
Good luck! Let us know how it turns out.