Haha well let's just say you'll get what you pay for...But your Viair P450 is already 250€, which I find is a lot considering the low performances...Just add another 250€ to the basket and go for a CKMTA12 like I have...It's powerful but not so big, like 30x30x15cm, so it could fit below your jack mount I think, you can wire it to one of the AUX upfitters (the compressor is also delivered with its own relay and switch if you want)...The fit and finish of these compressors is really nice...
About the tank, it's not absolutely needed for tire inflation ; initially I didn't buy the tank and made my first marocco trip without it, it went fine and inflation is already pretty quick (1min from 1bar to 2.5bar...)
Adding a tank gives you a little more reserve so inflation will be a little bit faster, and you could even use an impact wrench, blower or whatsoever pneumatic tools...The bigger the tank is, the faster it will...I have a 4L tank under the hood, will show you some pics tonight...You could also install it below the cabin along the frame...
And dude, seriously, 1200€ for a train horn ?? You want to scare the camels away ??