I don't see any reason you can't hand wash the liner. A little soap and water is not going to make it fall apart!
As far as the leather itself, I don't do anything but wear it a lot. This is gross, but I think you own sweat, oils, etc that get into your leather from the inside keep it moist, healthy and supple. As long as it doesn't get junky, just keep wearing it. I do think it's important to hang your gear up and let it air dry with good ventilation. If you do that, it shouldn't get too stinky.
To get bugs and stuff off the outside, I use Saddle Soap... what you would use for shoes, horse saddles, etc. It cleans and revitalizes leather!