I’ve got a Longitude for pretty much the same reasons as you.
I have a Tortec Epic Alloy rear rack mounted on the lower set of lugs to keep it nice and low. The most I’ve put on there is around 13Kg, which is nearly the weight of the bike itself. While it was really tough to carry up some steps, when riding I didn’t notice the weight.
My bike shop put some mudguards on it a few months back. I’ve taken them back off now (thanks to the fact I’ve been on dry trails more than expected).
When the guards were mounted, the rack was mounted on the higher rear mounting points and the guards on the lower. From memory, the guards needed quite a long bolt for the attachment point near the BB, while the other mounting point was on the rack! The shop mounted the mudguards using a bracket they made to the rear light fixing point on the rack.
I also found that when the chain was on the smallest chainring, the front derailleur touched the rear mudguard so it’s all a bit tight.
Anyway – I totally love the bike. I’m thinking of getting a slightly shorter stem as I’m 5ft11 and have the 19inch frame which I think is very slightly too long. I’m also thinking of putting some Big Apples on it as it’s mostly used for road/dry track.