My warband is level 10 now (the soldiers are level 7-9) - what's next?

Till now I haven't successfully completed a story mission, but investing XP and GK in soldiers who are actually ready for retirement doesn't make much sense to me.

On the other hand, doing the story missions with a new warband is not promising. What level the soldiers should have for the first story mission? I tried it once with level 3 and failed miserably...

Late to reply, but if it does not help you, maybe some other might be interested.

If you are afraid of loosing valuable man i read that it is possible to "save scum".
Go into extras in your Mordheim Gog overlay and choose to backup your cloud save.

The game regular saves can be found under:
"B:\USER\Documents\My Games\Mordheim"

If you are not satisfied with the outcome of the story mission. Delete the content of My Games\Mordheim Folder and replace the files with the backup Folder you find in your installation path (e.g. "G:\Games\GOG\Mordheim\!Downloads\!Cloud Sync Backup").

Have not tried it myself, but i see no reason why it should not work.

As said, it's a bit late, but this might help someone else.

It's not so much "what level?" as "what difficulty does it show?". When it becomes a "normal" mission, you're probably more than capable of handling it, assuming reasonable tactical skill. Equipment and training can modify the effectiveness of your troops compared to others of the same level, and that will affect the point value of your units. Depending on which faction you play, the mission map and opposing faction will vary, which also affects difficulty. The missions are rated at a fixed number of "points", so you should compare the point value of your own group (plus the faction's "notable" if present) against that number.

I did the first story mission at around level 3 and failed miserably, as the respawning opponents gradually wore my party down, while I had no idea how to get to where my remaining troops needed to go.. Following that defeat, the warband then took serious damage in the following mission, with one dead and two others permanently injured (not much point in a one-armed archer, or in a Magister who cannot cast spells due to "megalomania"), so I deleted the whole group and started over.

Second time, with the new warband, I did the mission at level 4, showing the difficulty as "Hard". I had a much better idea of where I was going before I went in, and was able to position the melee troops more effectively and give them some ranged fire support. I concentrated on taking out the high-level opponents, because only generic troops spawn as replacements, and was able to concentrate the group properly before advancing in force. Mission accomplished, no losses.

Some ideas:
1. Try to unlock all five trade-level bonuses for each of the 3 listed factions in the Smuggler's Den. This also unlocks new recruit options and you'll gain 'free' members to your warband among the rewards.
2. Beat all story missions, so as to unlock the "Campaign" task for your faction (and thus gain the most points to spend on Veteran Skills) in the Veteran System.
3. Try and find all purple rune formulas while on missions, and upgrade/customize your weapons/equipment to the best possible.
4. Bring along a new recruit on missions to quickly level them up while 'babysitting' them using your veterans. This way you can build up a pool of useful replacements should any veteran soldier need healing or retirement.
5. Play multi-player using your lvl 10 warband, and learn the hard way that your awesome builds against the AI suck in PVP. But this is a great way to learn to play better and get ideas for new builds.

Just make sure to keep plenty of Wyrdstone on hand to sell for cash for when you need it.

If your Warband is lvl 10, you should by now be seeing high-level heroes and henchies offered as new recruits. So if you need to retire someone, it shouldn't be a complete disaster (as long as you have cash to pay the hiring fee). When you hire them, you can spend points and train up their skills and spells for free, as long as you do it before leaving the hiring screen. So make sure you have a particular build in mind.