Play against Necropolis.

We will generate randomly, but with the maximum size.

Again, much depends on the template, but, as I understand it, you are not playing for a rush. In a random game, it is very important to quickly reach the "rich" zones - you will level up quickly and find money. Take Arghat, although Tilshek is easier at the start.

And which skills and abilities should be upgraded first?

You wrote everything correctly and in order. First, upgrade combat skills, then Silence, although there is a risk of being left without it. It is also worth taking Machines right away, because, judging by the description of your opponent's upgrades, he will not have Deadly Cold, and the Ballista will still cause him trouble.
The Orc will be significantly more mobile, and you need to take advantage of that.