Will start with "for detailed advice regarding your particular situation, please engage a lawyer or Treuhand experienced in this field." OK, now to the fun part:
One way to look at your GmbH is as a separate "person." This GmbH person will do the work for the bank, be liable if anything goes wrong, is responsible for its bills and debts, etc. Advise you keep all risk at this level. Toss out the Einzelfirma idea - besides the payroll hassle, you then open yourself up to be personally liable.
Since the GmbH "person" cannot make any decisions, a physical person(s) is designated as GF. You want to have written employment contract between GmbH and GF to protect yourself as GF. Compensation if only one part (you can even make salary variable, e.g. equal to monthly net after expenses so that you doing all the work get all the income.) What you really want in employment contract is that GmbH covers all personal liability for your decisions as GF excluding standard gross negligence, criminal behaviour, etc
Being shareholder + GF not that much different than being regular employee, except that you will not be eligible for unemployment (but have to pay ALV) and that if company gets in a big hole, you and partner as shareholders could be held personally liable for select debts of GmbH (like some payroll, taxes, etc.) in case of bankruptcy.
If GmbH employs anyone (even if just you) the GmbH still needs to have registration for statutory AHV/IV/EO, a Pensionskasse if any employee earns over CHF 21k/year, and supplemental insurances like KTG and UVG. You can do all this separate starting with your Kanton's Ausgleichkasse , but for small start-up consider joining your trade organisation, Gewerbeverband, or local Arbeitgeberverband. They can guide you to faster registrations and better group rates.
Yes, dividends are normally shared proportional to share participation. However, you can make separate agreement where your partner voluntarily forgoes any dividend payments. As general rule, you want lower salary and higher dividend due to social charges on salary and better tax treatment on dividend.
hope this helps, good luck with your new business!