Your greatest danger on the sidewalk isn't pedestrian accidents, though that's how you're most likely to injure someone else. (Especially if you expect ordinary pedestrians to respond predictably to "on your left" -- they aren't in conversation with you, they won't make out "on your", all they'll hear is "left", and a significant fraction of them will step to their left as requested.)

Your greatest danger on the sidewalk is from motor vehicles -- every driveway becomes, essentially, an uncontrolled intersection where motorists are not looking for vehicular traffic when they cross your path. If you're riding no faster than pedestrian speed, that won't be too much of an issue, because motorists crossing sidewalks generally are looking for pedestrian-speed traffic.

But if you're going any faster than a pedestrian, you're at significantly increased risk of being hit, either by a motorist pulling out of a driveway, or by one turning into a driveway.

At actual road intersections, again, if you move no faster than walking pace and obey all the pedestrian rules, you're not at great risk. But if you're entering the intersection faster than a pedestrian, motorists won't be looking for you coming off the sidewalk at vehicular speeds, so you're at greater risk from both cross-traffic and turning traffic.

You'll be much safer, have a faster commute, and reduce your stress level if you learn to control a lane of traffic on your bike. A safety course would be a good place to start -- google for CyclingSavvy or LAB courses near you. Having an experienced instructor lead you through safe traffic cycling skills will get you up to speed years faster than simply trying to learn it on your own.