It's hard to explain what would tear this car apart and what would not. For the last 3 years (including today) I have been soft wheeling my Golf on some of northern Nevada's an nor Cal's most remote wilderness areas. I am continually blown away and just laugh at what a heavy motor and front drive can get through and retrace to come back from. Even with an open diff.
It seems that you (op) have taken enough risk and have been enlightened to the capability of your car. You can wheel these cars if you take some precautions. They are not perfect, but not every body needs perfect.
Anytime you can remove a variable that has the potential to leave you stranded is money well spent.
1. Get a skid plate. Whether you are lifted no inches or 4 inches, you will hit. 2/3 seasons later, the terrain changes. Sometimes we just make poor judgment. Sooner or later you will hit.
2. Traction is your best friend. Disconnect one side of your swaybar (keep a 16mm wrench in the trunk) and let the suspension articulate. At the dirt trail entrance turn the wheel full lock in either direction, shut the car off, unbolt one swaybar link, pull it forward an inch or two, drop the bolt in the door pocket and go. It helps a lot. I've tried it both ways.
3. Tires. Get the most aggressive tread that works well for your area. Upsize to something reasonable (205/70, 205/75, 215/65, on 15" rims) b/c you will gain traction and a slight lift.
4. Lift. Since you will be navigating logging roads, I will assume you will be driving rutted terrain. Low clearance vehicles don't do well in this arena. This is where the skid plate will save your a$$. This is where traction will make you her b!tch. So, the more the better? How you achieve it is up to you.
5. Injectors. Bigger injectors offer more torque. Since you are driving a 5 spd, you will need more idle-3000 rpm torque to keep forward momentum. .205's are good, pp 520's are better. An alternative to injectors is to do the hammer mod to up your injection quantity. The larger wheels has a surprising effect (reduced) on first gear grunt.
6. LSD. Wavetrac would win my vote. The zero load = open diff behavior of Quaif/Peloquin does not turn me on. Please note: I have no experience with any of the above manufactures. They are cost prohibitive to me at the moment. But I read a lot....
Things I would not do:
1. Brakes. The ones that came on your car are fine. The expense of doing smaller brakes to get a taller tire sidewall imo is wasting your money and time. If you could put your energy into sourcing a tougher rack and pinion assembly and some stout ball joints/ tie rod ends, would be much more fruitful. The longevity and longer service interval would be better for your free time.
I'm also thinking that the taller sidewall on a 5.5" rim is not a great combo for on road driveability (the other 90+% of the time).
2. Trailer. The current crop of U.S. hitches (Hidden Hitch et.al.) all hang too low and drag. I ended up pulling mine off. It hit so much it was a little bent. Also, if you have to back out of a sticky situation and that thing hangs you up? Ooof. A euro hitch is your best bet but they are bucks. Not DOT legal either...
An alternative? Roof rack with a 30 something inch wide, 60 something inch long cargo box. That will fit your gear in it, I would think. Mine sure as hell does. And I can lock it all up.
I hope I don't sound like a fatherly know it all. These are things I have observed over the years. I figured I'd just through it out there.
No, these cars were not designed to do what Jeeps do. But, how many people max out the capacity of their Jeeps? The A4 body cars are surprisingly capable. I figure if you are scraping the underside of your car constantly, you are in the wrong vehicle. I only scrape every so often, so I justify it. I would rather max out the capacity of this car before I move on. The learning experience from driving properly and consciously is priceless.