You probably want to take it a little easy during breakin, but that does not mean babying it, just not full throttle max rpm for a few hours. Mainly you need to vary the rpm, load, and speed, during breakin. Try not to ride at the same speed/rpm until you have at least a hundred miles or so. Keep changing gears, rpm, and speeds. Avoid interstates or high traffic highways as you need to be on and off the throttle, and shifting frequently.
Manufacturer's vary widely on their recommendations, but all agree that you need a breakin time. Some recommend 500 miles while others recommend 1000 miles before going over some rpm limit of 50-75% of max. I agree that max rpm is not a good idea immediately, but don't think it needs to be limited for that long.
I like to break mine in like I intend to ride it, that means aggressively for me, high acceleration, high rpms, and high speeds. However I give it a 100 miles or so of tenderness before I start stretching the limits, but not too long that patterns are set up that you can't erase. Once you get through the initial breakin, you need to include full speed, full rpm, max acceleration in each gear, also to get the full breakin across the complete power band.
Some people say ride it like you plan to from the start, but I like to give it a little time, varying everything continuously until it has time to seat the rings, valves, bearings, etc. before I lean on it too hard. I gradually stretch the rpms in each gear with a 50% limit initially for the first few rides until I make the first oil change at 20-50 miles. Then 60% limit for awhile as phase 2, then 70%, 80%, 90%, and eventually 100% after the 2nd oil change at 100+ miles. I use short 10-20 mile rides or less, and let the bike cool down between phases, so it can go through the expansion and contraction heat cycle, gradually lengthening the ride in each new phase.
One thing that everyone recommends is that you let the bike warm up at idle first before each ride. NO revving of the engine while in neutral or with the clutched pulled and no load. Vary the speed, load, rpm, and gear for short rides, then let the bike cool off before repeating the cycle. NO long rides until it is broken in some, gradually lengthening the ride, and time between heat cycles.
Another important breakin requirement is an initial oil change. The Honda Service manual says the first oil change should be at 600 miles, but I don't know what the owners manual says. I agree with most other manufacturers that this is WAY TOO LONG to leave the breakin oil in the engine. You want to get all the metal filings from manufacture and those being worn off by the breakin out of the engine before they can cause any wear problems, and that is even more important for the Rebel since it has no oil filter. Other manufacturers recommend first oil change from 20-100 miles. I also change it whenever it is convenient between 20-50 miles. I change it again after another 100 miles, and then start the manufacturer's recommendation. After the first recommended oil change at 600 miles Honda recommends every 4000 miles, but most people think that is way too long with no oil filter. I change mine between 1000-2000 miles depending on usage, or annually if not riding it much.
One other item is the type of oil used during the breakin. Most everyone recommends against Synthetics until the bike is broken in, since they do such a good job of providing an oil film, that the rings may not seat, or at least take longer. Run the oil that came in the bike for 20-50 miles. Change it to 10W40 dinosaur oil for another 100 miles. Change again using 10W40 dinosaur oil for another 500 miles. Then switch to full synthetic like Royal Purple or Mobil 1 for the life of the bike. If you are in a cool northern climate 0W40 is my preference, but 5W40 or 10W40 work also. If you are in a hot southern climate like me I recommend 0W50, but 5W50, 10W50, and 15W50 also work well.
Hope this helps get you started, and enjoy the ride. I don't think you can really hurt a Rebel no matter how you break it in. I got my bike at 500 miles after 2 previous owners who were both beginner women, and I'm pretty sure they did not break it in like I ride it, but it seems fine.
1999 Honda Rebel CMX250C
2003 Harley Sportster 883 Hugger
1998 Harley FXDWG Dyna Wide Glide
ALL IN! GO TIGERS!