I have some customisation questions regarding the Xone42...

Q1. The X42 only has 2 phono inputs?  I've read you can convert a channel into phono.  If so, is this possible to do?
Q2. The crossfader... Does the 42 not have the capability to have a Penny & Giles fitted as an option?

A1: Most setups only utilise two RIAA turntable decks, though there are those specialists who use three or more.
Unfortunately, the Xone:42 doesn't cater for this directly, as you are correct in spotting that only two RIAA-biased PHONO inputs are provided.

You can mod a PHONO input to LINE by bypassing some components, but going the other way round requires the addition of special filter circuitry, so it is not practical to modify the mixer to do this unless you change the circuit board in the mixer for another PHONO / LINE input channel card.
This is worth considering if you can liaise with your supplier to arrange this or have this modified after-sale by a service centre.

Conceivably you could have 4 phono/line inputs in the Xone:42 by the special fitting of the input cards in the mixer...
Your mixer chassis would still be labelled as 2 phono/lines and 2 line/line inputs, and there is no easy way for us to change this, so you'd either have to remember, or make your own label!

A2: Yes, the Xone:42 can have an optional Penny + Giles crossfader fitted if you wish.
Page 26 of the Issue 4 Xone:42 User Guide lists this option as part number 002-719JIT.

Please note though, that since this User Guide was written, the Xone:42 is now available in a black (STORM GREY) front panel (see the website for more information and pictures of this).
Depending on your supplier, they may have slightly older silver front panel units in stock (worth checking first!!). The 002-719JIT option has a silver crossfader plate.
If the Xone:42 has a storm grey front panel; you would need the 003-914JIT P+G crossfader. This is only a cosmetic issue, but it could be possible to get the correct P+G option plate.

It might be worth arranging this to be pre-fitted to your mixer before delivery if your supplier is able to arrange that and is technically competent, but if this is not possible due to their stocking and supply arrangements, both modifications can be carried out after-sale by an authorised Service Centre.
Please note, however, that after-sales modification would be chargeable, so where you can it makes sense to discuss customisation pre-order!