Congrats on making an Escape your first RV!
As for water hoses, you basically only need to have one that states it is an 'RV/marine water hose'. They are commonly white like this
https://www.amazon.com/Legacy-Manufa...198577386&th=1 or we use one like this
https://www.amazon.com/Teknor-Apex-4...a-571811726537 . An RV/marine hose is all you need to fill your fresh water tank and it can also be used for city water hook-ups.
Another important item you should add to your hose (if you are hooking up to city water) is a water pressure regulator like this
https://www.amazon.com/Valterra-A01-...2205705&sr=8-7 Sometimes city water pressure is set quite high - too high for RV plumbing systems, so a regulator like this will ensure that the water pressure from your hose will be safe for your RV.
We also add a filter to our water hose like this
https://www.amazon.com/Camco-TastePU...s%2C192&sr=8-5
Yes, it is true - you do need to fill your water heater with water before turning it on. Here is a video that explains more about the hot water heater.
https://youtu.be/AzIXArtmNRE
As for how much to fill your tank during travel? That all depends on how you camp. First, a reminder that water is a 'heavy' supply to carry. A full tank of fresh water will add hundreds of pounds to your trailer. So our general rule of thumb is to carry some (around 1/3 tank) so we can use some water to flush the toilet, etc while on the road. If we are planning on dry camping, we fill it up all the way, unless we know the campground has a water spigot - then I prefer to travel with less water and fill up when we get there.
Hope this helps. -Bea