In Mnemonica, Tamariz has a great way to learn the order and the number. That alone makes the book worth getting.
I have started using Mnemonica after using my own stack for a decade, so because of that I don't use Tamariz memorization method. I'm switching to Mnemonica mainly because of the sheer volume of tricks and effects that have been developed for it over the years.
Juan's memorization technique would definitely work for people with a particular skill, but I just wanted to mention that if you blend mnemonics with the pegging system, it helps for much faster recall for both position -> card, and card -> position.
For example, the first Mnemonica card is a 4C. In Derren Brown's mnemonic system (which is what I use), the 4 is an R, and so I think of the word CAR. (Club fouR) Since it is in the first position, I think of "formula 1 raceCaR" (which coincidentally also has a built in reminder of the number 4 in the word FORmula, and RACECAR has 4C in it *twice*). Now when I hear the number 1, I automatically know it's the 4C, and vice versa.
As Juan mentions in his books though, once you memorize it and practice enough, you make the connection so fast you may eventually forget your memory aids. For that reason, I practice my hints regularly and intentionally, even though most of the time I make the associations before the aid even comes to mind. Over time it is easy to start mixing things up, since you think of cards in so many other contexts and orders. So as long as you don't forget your memory aids even after you feel you don't need them anymore, you'll retain the memdeck order indefinitely.
It's a good idea to know a few different memorization techniques so they never get mixed up anyway. You could use Juan's method for memorizing Mnemonica, and Derren Brown's method for Sorenson's, etc etc, and never worry about accidentally muddling them up.