I'm paranoid about water damage, as my neighbor's house was destroyed after an upstairs pipe burst while she was away and her furnace stopped working.

My routine for when I'm away from my house any longer than an overnight, is to shut the main before the meter, lower the hot water heater to pilot only, then open an upstairs bathroom faucet (I do not have an expansion tank and I do not have a check valve at the main). This way, the system can expand or contract as necessary as the water heater temperature changes, but I don't have to deal with purging the air out of my pipes every time I come home and turn everything on again. There's only a little bit of air in the sink line and that purges in 2 seconds. In the unlikely event of a pipe freeze, I have at most about a gallon of water spread across the pipes in the house (not including the hot water tank), nothing that can cause damage to the house.

I noticed that the hot water tank expands under pressure, I can hear it contract when I release the pressure and I can hear it expand upon repressurizing it. I'm wondering whether there is a long-term effect of doing this repeatedly. Will it weaken the tank?

Would anyone recommend modifications to this routine? I'm paranoid but also like to strike a balance with ease and convenience.

you don't have to open a faucet if the water heater is set to pilot.
you are doing no harm to the tank by turning off the main..