Mackowski

Hi All.
I have 2 months old Trek Marlin 8. I have used it for commuting as its winter and felt more confident (amateur) riding it then my hybrid with thin tyres. Just after Xmas I have took it for a 30mile drive and my idiotism and lack of experience sent me down very muddy (knee deep at times) ways. I have finished the ride with the bike pretty much submerged in the water as some areas were badly flooded. It only went in for a split second and up to the top tube.
I have washed and dried the bike when returned home.
Rear cassette all scratched from mud and rocks - this shouldn't be a problem, right?
Noticed resistance when trying to move the crank with my hand, took it apart and noticed rust on the inside of the bottom bracket (Truvativ Powerspline, 73 mm, threaded cartridge) after I have removed it fair bit of water came out of the actual bottom bracket, now this is a problem right?

I cant take the time back as I am really annoyed with myself but I guess we live to learn and its all good as long as we dont make the same mistake twice. Will definitely plan my routes better from now on and maybe carry the bike instead of submerging it in the water.
Anyhow, cassette I will leave I think and replace only if it will start causing any issues which I hope it won't.
Bottom bracket I have no problem replacing. Will replace like for like at the moment as not able to replace the cranks just now.
This is my first bike with front suspension. Do I need to do anything with the forks? Take it apart to make sure there is no water in there?
Can someone recommend some mudguards please?

Thank you for your time
Mack