Identifying electronic components in Robotale Electronics fans package
I think your assumptions are correct. Going from left to right and based on something I found describing that kit as including one active and one passive buzzer:


That appears to be a potentiometer and the 103 marking will mean it's a 10K pot.
That looks likes it would be the 'active' buzzer that includes a driver circuit because it's larger and includes a positive designator on the label. Unless it's marked and/or you can get a datasheet from the supplier I can't think of a good way to determine the voltage, but considering it's described as being useful with Arduinos I'd try applying 5 V and measure the current it uses to make sure it's not more than an I/O line can supply (if that's how you'll be using it).
Yes that looks like an RGB LED. It might be a common cathode or anode and without a datasheet once again you'll probably have to do some testing but this answer about probing 7-segment displays could be applied to that as well.
The last one I'd suspect is the 'passive' buzzer that will just be a piezo element without a driver. They need an AC driver of some sort and it's probably safest to use a transistor for those such as detailed in the question Is this a proper way to connect a piezo speaker to MCU?


So you'll have some experimentation to do and without datasheets and part numbers getting the exact specifications of components can be difficult to impossible. 

While it can cost a little more sometimes while learning it can be less frustrating to start with components of a known origin and most of the more professional suppliers like Digikey and Element 14 are quite easy to deal with even for low volumes. Especially once you get a feel for the components that will be most useful to have on hand and you're ordering a few things at the same time to offset postage.