Hard tail with front shock works best. Rigid front fork will hurt. The best tyres in my experience is Maxxiss Crossmark.

The downside to an A4 size map board is that it takes up and blocks off a lot of handlebar real estate space. The upside is a bigger map is easier to decipher, and less changing pages. That being said, unless you know the route (then you don’t really need a map visual all the time) you tend to stop at each intersection/ change in route to make sure you are correct. Easy then to pick, check, turn over etc. I will probably use 3 in future, but do know the route now.

Nice. I don't have the time. May do RTP and join up...

No, but I see you are....?

On every training ride I would find a steep hill and carry / push my bike. I always trained fully loaded to get accustomed to the weight and feel of riding with a load. i also tried as far as possible to find rough rocky paths to walk on carrying your bike. The majority of the RASA trails are not smooth. Ankles and knees need to get used to it.

Make sure you train carrying and pushing your bike.

Backpack is better. When portaging, bike rests on it. Too much weight on the bike makes it difficult to lift over gates and fences. Plenty of those. Some riders do have saddle bags that they put into a backpack on the long portages. Also an option. I went with two feedbags on the handle bars, spares bag under the seat and a 5kg backpack on a hardtail and it was fine.

As a first time rider the A4 map board is essential. Carrying maps in a pocket or pouch is a pain. As you need to stop and take them out, look and put away. At night and with cold hands, gloves etc its an unnecessary hassle. On the board is a quick glance.

I used drop bars and they were perfect. No issue on the technical sections. Great for different hand positions and fantastic when getting over a 2 meter fence.

Your Salsa will be perfect. You need to consider putting a front shock on though. I rode a Curve Titanium hard tail with a front shock. Two feed bags and a tool bag we’re on the bike, the rest in a backpack. I used a 20L Deuter, but 25 would be better. The majority of roads (probably 80%) are non-technical dirt tracks, farm roads, and districts roads.You do need to be comfortable riding technical tracks as there are a few sections that will test you. Short enough to walk though if you have to. Other than that your bike choice is good.