I have posted on this before, and I am sure that a search would provide the same info, but ...
Fencing, as tall as you can have under your zoning, and certainly nothing under 6'. 8' is better if you can have it. Chain link, not cosmetic crud - you want to make the unwelcome stop as far from your house as possible. If someone can get to your door/window/wall without you making an effort to allow it, or if they feel welcome to try it, you're missing out. The gates must be locked at all times except to go through them, just as with any door or window.
Lights: timer, motion detector, whatever you prefer.
Camera: not a direct help, but if you can get a record of attempts, or probes of your system, the cops might get farther. Thursday AM when I went out to walk Teddy, there were prints near my house as if someone had considered trying to enter over the gates or trying the garage door. Other neighbors did too, and the majority of the tracks looked as if the person making them was trying to obscure them as much as possible in the small amount of fresh snow.
Cops: Make sure you have a good idea of the realistic response times, and if you have a regular district officer/deputy, ask to have him/her come by so they get to know you before the excrement is in the air circulation device. They so rarely get to meet decent people under decent circumstances that you might be appreciated, especially if you have good strong coffee and some pie.
Physical capacity is a major issue. I have seen articles about "old man guns" from BTDT guys. They are not looking forward to the day when a .22 is the best they can handle, but they have the plans anyway. The real world of ballistic performance, in which a pistol is what you use when you have no specific reason to expect a problem and a long gun is a better choice, can be trumped by your physical ability. Our next house will be single story, and not so big, in part for those reasons. (I'll be 60 soon, and am still pretty big and active, but time is not one's friend.)
Buy and read and re-read a copy of
CAP - In Defense of Self and Others . . .: Issues, Facts & Fallacies -- The Realities of Law Enforcement's Use of Deadly Force, Third Edition (9781611636826). Authors: Urey W. Patrick, John C. Hall. Carolina Academic Press. While directed at LE specific issues, many of the principles about ballistic performance, the time constraints, and the like are the same. I am sure you can get it cheaper on Amazon or some other location, but even at full price, the investment in knowledge is easily worthwhile.
Dogs: I like dogs. I like larger protective dogs. Most of our dogs have been Rotts and Rott X. My life is set up to allow for them. Note my avatar - Bozo was a RottXFila and that muzzle was not for show. He took after the Fila temperament - loved us and his canine sister but HATED everyone else. (He did have some dog and horse friends, too.) Not all that big at 125 pounds, but strong, and truly dangerous. You might, with a really savvy dog person, find a breed that will suffice but also be within your physical capacity, but if you you do, that research will be a pain. I know some recommend the Great Dane as they do not need a lot of exercise. My impression is that a true protection capable dog breed will be outside of your physical capacity. An alert dog serving as an alarm might be as good as it gets.
Guns are the last layer, and hopefully the least important. One of the advantages of all the previous layers is that it will be easy to show that someone who goes through them will not be someone making a "mistake", but undoubtedly a violent criminal. Get enough training to be able to deliver rapid accurate fire with a controllable firearm. As noted, a .38/9mm pistol platform is about as good a compromise as you will find. In a traditional revolver caliber, I am a fan of semi-wadcutters at modest velocity and at the upper level of weight for caliber.
Given your description of your capacity, I am not a fan of the shotgun. It does have a relatively complex manual of arms, is relatively heavy, and with service ammo will kick a good bit. It is not a point and shoot area weapon, contrary to myth. (And slugs are generally the default, as I was taught in my academy.) In reality, a quality AR with good ammo, a sling, light, and red dot (Aimpoint) is a very good choice. Relatively light, easy to shoot, and among the least likely platforms to "over-penetrate" (an overblown risk, but not zero risk). Long guns do present a greater problem in close quarters weapon retention. Given your capabilities, you have no business engaging in hand to hand conflict with anyone over 10 or so. Anyone who gets through your door needs to be shot, and long before they can make contact with you. Where I live and work, no one would GAF at all about you shooting in that manner. Other places may not be so enlightened. Know your political and legal environment. (Reading that book and getting training allows you to articulate the risk presented to YOU by almost anyone, part of the process of defending yourself legally.) Don't bluff, or talk, or screw around - if they don't turn and run at first sight of you, you have a clear and imminent life threatening problem. Mindset is critical - you need to understand the nature of the offender and what you need to do to prevail.
As noted above, social media such as FB, Instagram and the like are not your friend. Anyone you know, friends or family, needs to have strict directions to never mention you in any way at any time. If they ever do, never tell them anything again.
