Regarding company overhead expenses it depends a lot from what is going on in the company and from the provider (there are cheaper and gold plated).
You’ll have:
cost of keeping accounts
cost of preparing annual tax declaration
calculating salary and handle AHV payments
then potentially VAT, Stamp Duty compliance
If you want my guess for all of the above excluding Stamp Duty (which you could do yourself) it would be 3-5k CHF depending on provider and number of transactions/billings.
If you can opt out of being audited (if your other partners/investors don’t mind), you save 10k CHF for an audit (Revision). You do it when you set up the company (Verzicht auf Revisions, Opt-out).