Looking for tourist office at London Heathrow

Terminal 5 is the newest terminal and is apart from the other terminals. 20mins sounds about right (or even a bit quick).

Why do you want a tourist office? There are a few, but not many, in central London, notably at Victoria and near St Paul’s. But you can find most things online or here.

Why do you need a tourist office? What information are you seeking?

Heathrow is huge so 20 minutes isn’t bad.

It will be a jaunt to get to the Heathrow Express. I’ve done it many times as I’ve stayed in the Paddington neighborhood for years. I fly Virgin Atlantic so I arrive at Terminal 3. Thankfully there are people movers. Remember to stand on the right to let others pass by.

Are you staying in the Paddington neighborhood?

I'm getting some oyster cards from a friend and hoped to top them off, plus get a new map (although things haven't moved around much in London since my visit in 1984 - although the map has both East and West German embassies noted) and maybe some information about Thames river cruises - something I haven't bothered to research yet.

My hotel is the Roseate a short walk from Paddington.

You can top the Oyster Cards up at the ticket machines at the Elizabeth Line/HEx station.

I would just board the HEx at Terminal 5 and go into the WH Smith bookshop at Paddington for a current map book.

British Airways uses terminal 5. You can top off the Oyster cards there. After clearing immigration and getting your bags, follow the signs for the underground, Heathrow Express, and ground transportation. There are machines there to top off the cards. Tube stations have paper pocket tube maps if you need one, or you can download a pdf version to your phone.

No idea about getting a paper map since not many people use them anymore. No need to spend time going to a different terminal just for a map. You could buy one at a bookstore before going over, or as stated above.

Thanks everyone. Directly to the Hex it is

The Heathow Express is directly below T5. No long walk at all.

Before you buy a map, ask at your hotel. They probably have one.

You can buy a map of London here from Rick's store:
https://store.ricksteves.com/shop/p/streetwise-city-maps
It will be mailed to you promptly, giving you time to study it before your trip.
It's a good idea to take a good look at it before you leave home, learning where the neighborhoods, parks, and attractions are. This will help you get your bearings once you're there.

maybe some information about Thames river cruises - something I haven't bothered to research yet.

The Thames Clipper/Uber boats travel to many locations along the Thames River. These are used for transportation by tourists and locals; there is no narration or guide onboard.
The good part is you just tap your Oyster card when you get on to pay, tap again when you get off the boat to end the journey. The ride is not expensive. You get to see the same scenery and buildings along the river that you get from the other tourist boats that cost more to ride.

Route map:
https://www.thamesclippers.com/plan-your-journey/route-map

For a good look at London by water, board this boat in the Westminster area and ride it all the way to the Tower Of London pier. Another interesting route is from the Tower Of London pier to Greenwich.

It is important to be aware that although you can use Oyster or contactless on river journeys (or the Cable Car) such journeys fall outwith of the daily and weekly cap.
You should also do a fare check of your intended river use that day as a Hop On Hop Off ticket for the day of £25.40 Adult, £50.80 family may work out as the cheaper option. Those are the buy ahead less than 7 days prices, higher as walk up fares.
But with 25% off if you buy more than 7 days ahead.
For instance a single fare from Central London to Greenwich is £10.80. Buy that return as a Hop on Hop Off daily a week ahead and you have already saved money before any other journeys.

There are no child fares either with Oyster PAYG.

Convenience is not always the best policy.