I can’t speak about specifics to that bike, but I did it last year on a Trek SC.

Super easy to do if you’re comfortable doing basic wrenching on your bike. And if not there are YouTube videos to help out.

I didn’t order a kit, but ordered separate components from competitive cyclist. They had all their stuff on sale when I did it and it was ~$900 for everything, including the brake lever shifters.

Some of the stuff is on sale right now as I was considering upgrading my wife’s bike, but doesn’t seem to be as cheap as last year. I’m coming out to over $1k to do upgrade.

Di2 is a moderate effort Di2 if you are comfortable doing any level of bike maintenance. I did my Felt IA16 earlier this year with all new Ultegra 8000 stuff (and a couple Dura Ace bits). Total cost was around $1,500. I got it all from Bicycle Doctor. I could have saved a few dollars by buying the cheapest from several European parts companies (Merlin, Wiggle, etc.), but I preferred working with BD to verify my parts, the faster delivery, and true US market support. The savings from Europe at the time was not that huge (maybe a couple hundred dollars at most).

There is no kit for a TT bike. That is unfortunate, because it would greatly simplify the purchase. Plus, you have to design and measure your specific wire layout and lengths anyway. So, plan for lots of planning.

The one thing to confirm ahead with your B14 is how compatible it is with Di2. Meaning, you will want to have the wires internally routed as much as possible, and ideally mount the battery internally. I believe the current generation B series is fully Di2 compatible for internal routing, but I am not sure about earlier generations. If you have external routing that bugs you, eTap might be a better match. (I put eTap on my road bike for this reason... the shift cables were 100% external from the head tube to the derailleurs.)

Yes, I upgraded my B14 to di2, here is my thread:
https://forum.slowtwitch.com/forum/?post=6479150
I'll be happy to answer any questions you have, I changed the aerobar to an alpha x so I could hide everything but it is not necessary.
It was a pretty straight forward installation which I did myself.
Here is the component list I used:
Rear derailleur: RD-6870
Front derailleur: FD-6870
Tri shifters: SW-R671
Brake shifters: ST-6871
A junction: EW-RS910 (in the extension)
Battery: BT-DN110 (in the seatpost)
B junctions (1) SM-JC41, (1)SM-BCT1 (one in the frame, one in the aerobar)
Misc. e-tube wires

What was the total cost of your build?

I haven't purchased everything yet, but have all the major components outside of the battery.

I just shop the classified section. I think I'm only in like 350-400 bucks so far and that's for front and rear derailleur (6780), brake lever/shifters (DA), and bar end shifters. All used, but not a scratch on them.

Plan to buy everything else new though. Will get battery and junctions soon. Plan to get a fit this fall and order cockpit based on that. Then I'll measure for wires. Thinking all in, I'll be in the 800 dollar range.

Add in about 1k for the cockpit and I think I have a pretty sweet IA16. Got the bike for 2350 (last years model), so all in will be around $4150 for a di2 bike with an upgraded cockpit. Better than paying over that for an IA10.

For all the Di2 components including cables and charger I paid $1020. Bought everything from competitive cyclist during black Friday last year.

I did similar set up 2 years ago on a B14 but with DA9070 vs Ultegra. only difference was they didn't yet have the bar end junction box so charging was a pita. used the internal A junction in my Alpha X and external B box underneath the BB. Still pretty clean with internal thru the downtube and then wired to rear derailleur along the chainstay. for sure a DIY job for anyone with modest skills. I also added the D Fly SM-EWW01so I can connect thru Bluetooth for Etube.