Dual GFCI/AFCI breaker to support regular TRR USB outlets on kitchen counter: to code?
You're not on NEC 2020 yet, unless your state just adopted it. (MA has so far). 

Under NEC 2017, Code requires GFCI only in certain places (kitchen being one of those) and it generally does not require AFCI breakers in those places. The rationale being that providing both can be a technical challenge. So you probably do not require AFCI protection in the wiring to a kitchen, but it is a good idea if (in order of importance) roached wiring, aluminum wiring, old wiring, or wiring in non-metallic cabling or conduit. IMO. 

Keep in mind despite the similar names, AFCI and GFCI do totally different things. AFCI protects wiring from burnup due to bad connections, and this mainly guards in-wall wiring, particularly backstab connections. Originally they were conceived to protect electric blankets, but "backstabs in plastic boxes" proved to be the main thing AFCIs defend from.  Whereas GFCI protects humans from shock, hence the requirement anywhere within reach of a sink.  

AFCI is only constructive at the breaker.  GFCI can be anywhere, however. And at the breaker is just fine.  Your plan is perfectly fine. 

Keep in mind that making an outlet USB does not erase any requirement for Tamper Resistance.  If TR is a requirement, then you need a recep that is TR and USB. There is a lot of junk on sale on Amazon Marketplace and other outlets of the Alibaba junkstream, which uses direct mail to circumvent the laws which assure the supply chain contains safe, UL-listed products.  Such things are best bought at a bricks-and-mortar retailer; if you don't like Home Depot's pricing, try a genuine electrical supply. 

Do your level best to keep refrigerators, freezers, fire alarms, radon systems and other "needs power for safety" appliances away from both GFCI and AFCI.