Is my bike getting ruined?
Chain will rust always after washing (or even light rain or a puddle of water), if not re-lubed. I think this is detrimental to the chain, as it removes material from the rollers and thus contributes to chain stretch.

Bolts for stem, handlebars etc. seem to always like to rust after rain or washing. I don't think it is a big deal, but it ruins the look of the bike. How I solve this is put a small amount of grease at the bottom of the bolt head (and then wipe any excess). The grease seals the hollow head and stops rust. Using a hex on the bolt removes most of the grease, so re-lubing after repairs is nice.

About the disc brake rotors - this surprises me. Apart from two general advices, I can't see how can I help with this. Firstly, after washing a bike, lift it up several times and force it into the ground - this should should shake a lot of water off. Secondly, after that, you can make a couple of hard stops - the disk pads will dry the disks in no time.