That deal sounds very dear to me, I got a similar deal but mine was a 3ft wooden viv for my royal and she was fine going straight into it when she first came home.
The main thing you need to watch is that they have the correct heats otherwise they can be very very fussy feeders. I'm lucky as my Royal has only refused once in 3 years.
You can pick up wooden vivs on the net for about £50 and the stats for about £20, heat mats vary dependent on size and substrate can vary. I would suggest putting the snake into the viv straight away, as long as the viv is not too big for the size of the snake you get or they can get distressed. Make sure that there are a few hiding places and things for them to climb on. You should also be putting a daylight basking lamp in for the snake during the day, mine is on a 12 hour timer so it simulates day and night which also reduces the chance of feeding problems. The cold end wont be very cold but it will be cooler than the warm end as the heat from the heat mat tends to stay in the area that the heat mat is placed.
I usually pay about £1.50 for my rats, I think the mice are around the £1 mark depending on the size of them but as soon as the royal is big enough get it on rats as they get more nutrients from a rat.
Other than that as long as you have read up about everything you should be ok, if you want to have a look at the viv packs i got then go to Snake Kit CS1 (24" Wooden Viv Kit)
and i think they deliver as well. You will need to make a guard for the light though but i made mine out of chicken wire - cheap and cheerful!
Hope some of this helps!