Usually I try get some better brothers fast. They have better stats and usually better equipment.
Better defence and melee skills are essential. If you have less brothers all your guys level faster.
Then just add another higher tier mercenary.
Few easy missions and I can get few solid characters with decent weapons then its hard to lose unless you charge at large amount of orcs.
On start better focus on few good guys than large number of weak under equipped.
Or so I learn.
There is currently no reason to not get professionals soon as possible.