How would you handle a baseline corruption and insanity for the creation of a warband of a higher xp value and the normal 1000xp?

I was considering something like a d10 per 1000xp past the 1000xp baseline in either insanity or corruption.

Anyone handled this?

I had a situation where I offered the player to choose between 1 and 4 dices and distribute the dices before rolling on either insanity or corruption. The total sum from the dice rolls was also added to influence.

Ask yourself why you're wanting to start out with high level characters. Are you doing this because you want them to face high level threats? If that's the case, there's no real reason to have your characters start out with corruption. The high level of threats they'll be facing will cause quick damage to them. Are you considering balancing the starting power with extra corruption and insanity? Don't bother on that. The corruption and sanity systems aren't balancing mechanisms so much as narrative tools to represent the characters decay. For that reason, it's also better to not have the characters start out with extra corruption, as that takes away the opportunity to see them get morally decayed. Also, consider NPC profiles from the books. Look at the high levels NPCs. They're all bereft of corruption and insanity. Just start the players off like that, then give them high level threats to face.

If you want some mechanical advice and are deadset on increasing corruption and insanity, just add an extra d10s worth any time you inflict extra corruption/insanity.

Also, if you're doing this on a player by player basis, an still want to increase corruption/insanity to start, have it feed into a pool for all of the players so that each extra amount the players get, the more they mess up the rest of the party.

I can see from a "numbers and balance" point of view that you should take into account starting corruption and insanity and that you would want all the pc's to start out with more or less the same level.

However, from a not "numbers and balance" point of view this seems silly. The mechanical advantages and disadvantages are pretty limited at lower levels of insanity/corruption. So differences between pc's would have minor consequences. In stead, I'd adopt another approach. Since the characters have a lot of xp under their belt, they should also have an interesting story on how they came to be that experienced. In my opinion it would strengthen the roleplaying possibilities if you adjusted the level of insanity and corruption on the pc's background. If you specificly ask your players to think about possible sources of insanity or corruption, I'm sure their imagination will be stirred.

I'm betting that with at least to one of them you'll have to say: "Yeah, I get that you dabbled with daemonhosts and so on, but putting your corruption over 50 is probably not a good idea."

Ask yourself why you're wanting to start out with high level characters.

I'm recreating an old party from DH1 in Second Edition. They previously had corruption and insanity, but I wanted to give them a break and give them the possibility of less. Actually now that I think about it I might just have them roll a xd10 x being the tens digit of their previous character minimum one.