Congrats on the purchase mate, bet you're like a kid at Christmas today
You are going to be the most handy truckmount servicing person! At first it is daunting, but as you learn bit by bit about how they work, the mystery unravels. I'm not exactly technically minded but have come to understand the basics of a TM's operation and what the bits do.
If the machine has been sat doing nothing for ages, and from memory of the pictures it has due to the dust on it, I think it would be well worth you taking it down to Hydramaster for a good once-over.
I'd register on truckmounters.com because there are lots of hydramaster users on there, and plenty of guys who have, or have had, the same machine. Don't feel silly because you know nothing, we all start there. By asking the right people the right questions you can build up your knowledge and start off by doing little things. Then once you know your machine a bit better you won't feel so daunted if you have to do something a bit more major like change/repair the pump for example.
Luckily after 18 months of owning my machine from new there's been very little wrong that I've needed to fix. I took it back for one minor warranty repair and have been stupid enough to boil it dry of coolant but that's the extent of the problems.
I get my local mechanic to do the oil/filter changes, largely because he can dispose of the used oil & filters which would be a problem for me if I did it myself. Anything engine-wise either a car mechanic or other local place should be able to sort it (don't know what engine is in your machine but you'll get that info straight from other owners of the same machine).