Question 1) I remember hearing somewhere that if the cassette gets replaced the chain and rings also need to be replaced. The current chain is in need of replacing and the cassette is just about to explode (the cogs move on the spindle just by moving with bare hands) but the chain rings still look fairly good. Should I just bite the bullet and replace the whole drive train at the same time?

Question 2) Any recommendations on bash guards to replace the big ring? There is nowhere around here to use the big ring anyway, but lots of rocks and roots to get it stuck in.

Thanks in advance for any advice.

Not a expert on the subject but from everything I have read you "should" replace all.
I changed my cassette a while back to change gearing and didn't replace anything else. Then just a month ago I tossed a new chain on since it was stretched and didn't replace anything else also so I'm not following my own advise. I personally believe that if it looks good keep running it but keep in mind that it has the same wear as all the other components. Maybe it's a good time to change to a different set up like 2X10 if your running a 9 speed. Good luck

_________________
You never know what tomorrow will bring so go ride your EBike today or walk your pooch
Fear the Yeti
"Go ride your bike today, don't let the old man in.."

Mike

Chain and cassette together usually is good enough; if it skips after that change then you need to change the rings up front. If you are going 2x9 it would be a good time to change the rings and go with a different gear ratio.
The bashguard needs to be compatible with the size of the middle ring.

_________________
"Just stop this walking shit and let's get this done"
Avidtesty (Arch 2019)

Yeah, might not need to replace rings. Try and see. But yeah, good time to check 2x9 options. Go to an internet site with a big inventory listed (Blue Sky, Universal Cycles, Bike Bling) and see what your choices are for rings for your particular crankset. Go to Sheldon Brown's site for the gear calculator to see what effect ring size changes will have on overall gearing and spacing. Do you feel strong and want to go fast, or do you want to keep your existing low granny? In my case, I'm not strong, so I just increased my mid ring from 32 to 34, but I bought a 36T bash, in case I want to bump up to 36 later. Net result was I lost only 26th & 27th gear from the spread and rarely miss 'em.

_________________
Thus, if we are to understand the world, we should live somewhere between judgement and amazement — Alfredo Lopez Austin

Depends on how old your chain is. I am on my seventh chain with this drivetrain. Yes, seventh. I have a Park Took Chain Checker and replace when it hits .75. Much past that and you will be replacing the cassette and rings with the chain which is obviously exponentially more expensive. You will know immediately after you replace the chain if the other components need to be replaced.

Thanks all for your input and thoughs. Think just replacing the cassette and chain will work.

Any recommendations on bashguards? MRP, RaceFace?

BBG Bashguards - not necessarily the beefiest out there, but they're light, cheap, and have a decent selection of sizes, styles, and colors.