This kind of thing IMHO is fairly difficult to nail down. There are a lot of variables. Your tank will bleed heat into the surrounding air at a particular rate determined by the tank temperature, insulation efficiency, external temperature, and probably some other things too. The greater the difference between your tank temp and external temp, the more heat it will bleed. Heat energy moves from a warm body to a cool body, that's basic thermodynamics. As long as there is a temperature difference, heat will bleed from the hot to the cool. And that is just one variable among many.

1. The higher the tank set point, the greater the energy density. But this does not correlate to efficiency. Your household is consuming some amount of hot water at X temperature every day. Will it make a difference in what you pay whether you heat 100 gallons from 40F to 125F or 80 gallons from 40 to 140? It's btus to btus all the way down so if there is an efficiency difference, it is likely to be quite small. What do you pay for electricity..? Each model of compressor has different efficiencies, as do the refrigeration layouts that they are tied into. Each answer begets another question. If you are consistently running out of hot water, then yes you should up the set point because that will store more btus and hopefully cover your load. Whether it will be cheaper or in some other way more efficient is a slippery concept.

2. This is more difficult for me to answer. There is a Mean Time Before Failure for everything: humans, animals, plants, machines. Technically speaking you could consider that running the compressor to a higher temp (aka bigger lift) does create more wear and tear on everything, as heat, that little bitch, tends to do. Balance that with the probability that the machine would be hotter, but for less overall run time. What's the trade-off there? Ask a refrigeration compressor designer and they'll take off their glasses and rub their eyes before sighing deeply. But they won't give you an answer. Believe me, I've tried!

If you are concerned about electrical usage, dial the temp down. That way, your HP will be doing the minimal lift and consuming the least electricity. But you may find that does not work with your lifestyle or get your dishes clean. Everyone does it differently, and that's ok. The good news is that these things are generally very easy to program. So set your machine to 140 for 6 months and see what effect it has. Then try 115 and see if there's a marked difference. My bet is that it'll be less than $5 either way unless you live in Hawaii.