i will be honest. I am nearly 50y/o and not in tip top shape either. I have not owned a bike since I was 12y/o. I want to buy a bike. I am looking at the cruiser bikes. Most come with coaster brakes. I am not sure what to buy. I am new to biking, so I don't know. I have heard more positives about handle brakes but also heard a lot of things could go wrong, and what if I get stranded somewhere? What would I do? Please advise. Sorry if I am rambling.
There's a small chance you don't have as much hand/arm strength as you used to. A coaster brake provides a way to slow while leaving your arms free to focus on steering.
That said, a coaster brake is a rear brake only. The best stopping happens with the front brake, so ideally you'd have both, a coaster for the rear and a hand brake lever for the front.
Some consider it an unsafe practice to have just a coaster brake without also having a hand brake. The thought is that if the chain breaks you have no brake available at all. I would suggest you get a cruiser with a coaster brake and a front hand brake if this is a concern of yours.
Note: I have 4 cruisers with coaster brake only and ride daily. The coaster brake is very reliable for me, and I keep my chains oiled and properly tensioned so I do not fear that they will suddenly break.
Talk to your lbs (local bike store). Most will help you and not try to sell you more than you need. Avoid cheap department store bikes (bso). With hand brakes you have two so there is not a single point of failure and they are very reliable. If you are more comfortable with coaster brakes then that is good option also.
With hand-operated brake levers, there is a design feature that you have two brakes, not one. Thus, even if the front brake fails (very dangerous as the front brake is the primary brake), you still have the rear brake (providing equivalent stopping power to coaster brake).
Modern hydraulic brake levers require less hand force than cable-based levers of the past. Thus, if you want to stop quickly, the only thing that might limit you is flex in the system, i.e. lever reaching the bars. Bleed the brakes and most of this flex should go away. So even with weak hands, and high body weight, you can stop easily.
I don't think there's anything to worry about. With coaster brake, you only have the poor rear brake. With hand-operated brake levers, you have two brakes, one of which stops better than the rear coaster brake, and the other is there in case the primary front brake fails.
Hand-operated brake levers are easier to modulate than coaster brakes, and because they are disc brakes and not drum brakes (yes, even rim brake is a form of disc brake utilizing the rim as the brake disc), the relationship between application force and braking force is predictable (except for rim brakes you have poor stopping in rain until the rim becomes dry). With drum brakes, it may be hard to control to get exactly the amount of braking you need, partly because it's a drum brake and partly because the application occurs with feet and not hands. This combined with the very little force needed to make the rear wheel lock, means a coaster brake can be considered as an on-off brake and not a brake you can modulate.
Select a modern hydraulic disc brake system. It works perfectly in the rain and provides ample braking force. Also, disc brake wearable parts are very easy to replace in contrast to drum brakes that are hard to overhaul.
If you can get a bike with a decent internal gear hub (IGH) that contains a coaster brake plus a hand-actuated front brake, that's a excellent setup. Typical IGHs give you about seven gears that require next to no maintenance, and the included coaster brake is an extremely reliable backup brake.
Note however, that coaster brakes should mostly be used as backup brakes: They act on the rear wheel, and the rear wheel unloads as you brake. This unloading limits the effectiveness of the coaster brake. Also, it's hard to replace the braking surfaces within a worn-down coaster brake, so you don't want to put much wear on it. Nevertheless, a lightly used coaster brake easily saves you when your front wheel brake breaks (cable snapping, mostly). And you can be certain that you can actuate your backup brake as long as you are able to ride your bike at all, because the coaster brake is actuated via the chain without which you cannot ride your bike. This sets the coaster brake apart from a hand-operated backup brake which may get stuck without you noticing it, and thus fails you when you need it.
The combination front brake, IGH, coaster brake is especially useful because very easy to use, robust gear switching comes as a part of the package. There's no derailleur that can brake, chains generally cannot slip off IGH sprockets, etc. This is the perfect combination for people who are not much into biking yet, and want a worry-free bike. Don't go for 3 gear IGHs, their gears do not spread far enough to be really useful, but a 7 gear IGH is an excellent choice for casual riders.