I also like my rear rack rails to be horizontal, but if you use that rack on a couple different bikes, you might not want to hack saw off the front attachment rods if that might impair how it fits on other bikes. In that case, not quite horizontal is probably preferable. Or, if you did hacksaw them to fit, you can buy extra rods too. I think Racktime rods and Tubus rods are the same thing.
I have never bikepacked, but I have seen plenty of bikepackers, they carry very little gear. If you are carrying rear panniers, if you minimized your gear enough you might not need a front bag.
Four years ago I saw an article in a magazine on how to make a harness for bikepacking front bag. That magazine no longer exists but I looked to see if that article appeared anywhere else, and it did, here is the link:
https://dirtscrolls.com/14963349-how...lebar-hardness
I have not tried to replicate that harness, so I can't say if it is a good one or not. But with a good dry bag it might be all you need for a sleeping bag and some clothes shoved into the same bag. And if you are making it yourself, you can accommodate your bar width just fine. Make sure that you can shift if you put a bikepacking type bag in between your brifters.
Have you considered a suspension seatpost? I do not have a mountain bike, but I have on a couple occasions put a suspension fork and cheap telescoping suspension seatpost on my expedition bike and pretended it was a hard tail mountain bike. A friend of mind suggested the Thudbuster seatpost but I did not want to spend that much, instead I picked up a used cheap telescoping seatpost at a local bike charity for $10 USD.
Looks like you have 32 spokes front and rear. If you know how to use a spoke wrench, you might want to bring a few spare spokes. Odds are you will not need them, but if you do need one, you would really need it. Or, perhaps instead a fiberfix emergency spoke instead since that is not size specific like a spoke is.
You did not say how many days your trip is, minimize your weight as much as possible, if only half a week you can minimize pretty well. But, I have seen too many bikepackers show up in campsites badly dehydrated because they tried to reduce weight by taking too little water and ran out of water hours before they made it to teh campsite, that is a bad plan.
The one liter Smartwater brand water bottles fit well in bike cages, but only the one liter ones, the smaller ones do not. Life WTR brand one liter water bottles also fit well in cages. I only see one cage on your bike, how are you going to carry enough water?
Have a great time.