Eventually get the 12 for "balance". But I would also get 8 and 10 concert toms (if available in the line). Those will cost less than regular toms and actually be more useful imo.
Ultimately, I think all modern kits should have the 8,10 option - and with either or both 12/13. My icon kit came to me as an 8,10,13,14,15,16 mounted toms. But the ones I
played the most were always the 8,10,13. Never missed a 12 in 2 yrs of playing it. When a 12" finally showed up at very reasonable price, I bought it. But it really didn't add all
that much that the original 8,10,13 didn't already provide.
Back in the 1990's I had a Yamaha Recording Custom kit with 10, 12, 13, 14 and 16 toms. I experimented with various configurations and was surprised that I loved the 10/13/16 set up the most.
So no surprise where this is going . . . get the 10" tom. It's a great spread playing 10/13/16 to my ear.
BONUS RESPONSE: Definitely get a Jenkins-Martin snare drum! I have three different sizes/depths J-M and Blaemire snares and they are great. If you're only going to purchase one Jenkins-Martin snare
I'd recommend choosing whatever size snare is currently your favorite size/depth.