If you want a turnkey experience, an agent can provide that, and hopefully, you can find a good one.
But in this day and age, I'm not sure how much better an agent can do in securing better rates, and having the local knowledge, the two things that made them valuable in the past. I'm sure there are types of complex bookings, deals, and specific destinations where that kind of niche experience is still plenty valuable, but for a trip to Hong Kong or Tokyo, you can probably find all you need to know from your own online research, as long as you're willing to put in the time.
I haven't been to Tokyo in many years, but as a former British Colony, for English-speakers, language is largely a non-issue in HK.
Unlike many car-oriented cities, especially in the U.S., public transit is critical for the city to function, and they are willing to invest in it, so it is good, and cheap. Just grab an Octopus card when you arrive, and getting around will be very easy. Such IC cards like it, or the Oyster card in London, make it easy. Local prepaid SIM cards are cheap, for mobile access, if you don't want to pay your home carrier's usurious roaming rates.
The greatest concentration of hotels is at the southern part of the peninsula in TST, or the northern part of HK island, so that's where most tourists stay, and where the action is. Many are operated by the familiar American or European hotel chains, but even those that aren't won't be making you sleep on Tatami mats or use a pit toilet.
If you, or your kids are into car diecasts, or other toys like LEGO and figurines, I can suggest a place to check out.
While it's a touristy thing, do take the Star Ferry across the harbor channel, and sit on the upper deck (choose the right ramp) for the best view.
