You should be fine to mix them yes. Myself and many others have mixed a combination of the winestix together (two different types and toasts) in one carboy with more complex results. The stick should be just fine with a cube in there with it.

oak flavor may dissipate only a little over time. There is also the factor of when in the raising you add the stix. One should have an idea depending on the flavor profile expected if you know the fruit. To pull the sticks out too early might leave you with not enough. Assuming the manufacturers plateau for the product in a carboy is true If it becomes too strong wait only a few weeks more to pull them. You can always add a few cubes later but you can’t easily dilute an overoaked wine. You should be tasting and testing every month in the spring which puts you at the six months plateau according to winestix if you put them in sometime after fermentation completes but before cold stabilization.

I think the package recommends a minimum of six months but how long you leave them in beyond that is up to you and the flavor profile you’re aiming for. Taste at least monthly and make your determination based on that. A recent batch of Cabernet hit the mark for me at six months the longest I’ve tried thus far but at some point I may try up to a year.

At least 3 months. Longer is better.

up to you! That’s the great thing about home winemaking. You get to decide when there is enough oak for your tastes.

As long as is necessary to get the oak flavor you want.