Idiots guide as follows based on a Bav 36 setup.
Small amount of mast rake. Anywhere between 50 to 150mm at the gooseneck. You know when you have too much as the boat will have weather helm.
None of the shrouds should go slack when beating on the wind in approx 15 knots. Obviously the windward shrouds will be pretty tight and the leeward shrouds can be a little slacker but not much. They should not be flapping around. If the leewards feel almost as tight as the windward ones when beating thats about right. Don’t tighten them to get them as tight as the windward side because when you tack the new leeward shrouds will feel slacker and you will then want to tighten that. Do that too often and the boat starts to fold, or at least the forward bulkhead distorts and doors start jamming up.
Forestay also needs to be set right. When beating in say 15 knots again the deflection in the genoa luff should be less than say 75mm. If it looks more than that try winding on a bit more backstay. The mast and boat can take as much backstay as you can wind on on a Bav as the purchase is pretty low. Doubled mine to 24:1 last year to get a tighter forestay and better pointing. If the sag in the luff still exceeds 75mm with full backstay then the forestay is too short and needs sdjusting which is best left to a rigger unless you have an adjuster on it. Even so that can be a bit of a faff on the Furlex.
last point is obviously the mast needs to be straight left to right, No s bends. These can be a bit fiddly to take out if you don’t know what you are doing with the uppers and lowers so again may be best left to a rigger.
Sorry, now the last point. You probably don’t want to know all the intricacies of inducing pre bend for better sail shape in certain wind conditions but also check the mast alighnment fore and aft when under load. It does not want to be bending forward. This can be pretty terminal.
Hope that helps.

And having just reread your initial post the creak could just be that it’s a Bavaria. I used to have a creak on mine when walking down the starboard side and eventually pinpointed it to slight deflection on the deck that caused the underside of the deck moulding to creek against a bulkhead. Went on a diet and it stopped creaking!