Sounds like the kit has all the essential ingredients. I'm pleased to see there is a thermostat included, so many shops don't and it's an essential bit of kit! I think the price is pretty reasonable too, considering it includes the snake as well.
Faunariums are fine for royals, just make sure you have hides in the warm and cool ends so they don't feel over-exposed with the transparent sides. Faunariums also have huge amounts of ventilation, which can sometimes make retaining humidity an issue. Some people combat this my placing a damp towel over the vent holes, or by putting in a moist hide (e.g. margerine tub with damp spagnum moss in it). It may not be an issue, but some snakes need raised humidity around shed time to ensure the skin comes off in one piece.
Another issue with faunariums is that the lids do not 'lock' into place as they do with RUBs. You may need to strap the lid on with a couple of strong elastic bands to ensure your royal does not force the lid off - they are deceptively strong.
I'd also be temped to swap out the wood for another suitably sized hide - one where the snake can sit snugly touching the sides and ceiling.
I'd also, if it were me, spend a little more on the thermostat now, to save buying a new one when you trransfer the snake to a wooden viv. Assuming you plan to use a wooden viv in the end of course, I think the best method of heating it is by a ceramic bulb. If you do plan to go down the wooden viv/ceramic route then buying a pulse-proportional stat now will control the heatmat and also the ceramic further down the line - saving money in the long run!
I personally would initially avoid housing your royal in an adult-sized viv. Some people have moved there littles ones into a viv straight away with no issues, but I have heard of many tales of royals that refuse to eat in larger spaces, but begin eating again when moved back into a smaller RUB. Each snake is different, but I don't see any harm in playing safe and starting them in a smaller enclosure.
You also ask about how to keep the temperature gradient in your viv. You'd be suprised, but the difference between the hot and cool end can be dramatic. Especially with mats. Mats will only heat the substrate directly above them. They do not warm the ambient air and do not heat the cool end. Very little convection takes place though using a heat mat. You will probably find the cool end temperature actually drops to the ambient room temperature even though the heat mat is heating the warm end. (This is why I am a keep advocate of ceramic heating when using a wooden viv - ambient and cool end temperatures are actively heated also, something a mat doesn't manage).
Ceramic heating will still provide enough of a temperature difference between the warm end and the cool end.. mine are roughly a 10'c gradient. It may sound like a lot, but it's easy to achieve with a bit of trial and error with bulb placement.
There's a great post here about royal fasting:
And Custom Guards: Ceramic Heater Guards | Spotlight Guards | Reptile Heating & Lighting Guards | Vivarium Heater & Light Guards
will sort out all your bulb guard needs when the time comes.
Just for the sake of balance, I don't use any form of lighting as Wishlover does. The majority of snake keepers (certainly here on this forum anway) do not either. This is an example of different people doing things successfully in different way - which is part of the variety the hobby offers. If it works for Wishlover then great, but it isn't a necessity.