First, I feel the game mods should consider lowering the rank to unlock the Rescue Engine & Quint down from Captain to Lieutenant. It took me forever to make Lieutenant which I finally got promoted today.
That's not happening. The Rescue Engine and Quint are rewards for people who are more dedicated to the game. There are other threads that discuss this topic.
2. Who feels we should have a Pumper-Tanker for Engine and Tanker use?
Also not happening. Sebastian isn't a big fan of the combination units, as they make the game too easy.
3. An EMS Engine for both fire calls and medical services/transports?
Engines can already begin to treat patients. No, we're not making a combination engine/ambulance unit. Yes, I know they actually exist.
4. Fire boats for realistic water emergencies?
Hopefully, we'll see this soon.
5. The game mods should clarify what Apparatus is required when you gain more fire stations.
The only official sources of information are in-game and the Facebook page. Moderator and Administrator posts on this forum are also fairly reliable, though they often contain a good amount of opinion in them.
6. right now I own five fire stations and a Heavy Rescue is on my fleet and no calls have came up for needing it's use yet
You can get the "Burning Machine" mission at five fire stations which can require a heavy rescue. There are other missions that require heavy rescues at four fire stations, but they are either seasonal or have requirements of police or medical services.
7. What do I need to do?
Be patient and check out this page, which lists all the possible missions and their requirements (and can be found in the bottom right corner of your screen on desktop) https://www.missionchief.com/einsaetze