Do I go Deco Punk with my novel?

This is a bit early for your chosen time but I think it is a great -punk images and it was real...
Shorpy - Aeronauts 1910s

 

The main criteria for Deco Punk is that you add something that is fantastical. I could imagine your travelling group being in Paris and ordering some ailes de dragon à la sauce à l'ail [dragon wings with garlic sauce] or seeing a warning sign on a German autobahn screaming: ACHTUNG! Werwölfe bei Vollmond. Fahren Sie mit Vorsicht! [DANGER! Werewolves during full moon. Drive With Caution!]. In the Spanish Civil War your companions might see mages fighting with combat spells that sometimes go awry. Make the Loch Ness monster real and a lot more scary than what grainy photographs from that time period show. If it's late at night and everything's closed elsewhere in New York City they could go to Little Transylvania and order a bottle of a fine rare blood type with their ciorbă de burtă [sour tripe soup]. Maybe your travellers began their journey for different reasons but they meet a dying wizard descended directly from Merlin who tells them to find the original staff of Merlin and "return it to Camelot". There's all sorts of bad guys other than you-know-who to choose from in the Europe of the 1930s.

Go crazy and see what you can come up with.

 

Adela:
I was only tossing around a few random ideas but if your primary objective is to avoid the Great Depression and World War Two that is closer to alternate history. If you find a point of divergence from our history that prevents the Great Depression you automatically eliminate the rise of Hitler, the establishment of Nazi Germany and World War Two. Without the Great Depression the Nazis would've remained an obscure political party in the Reichstag and Hitler would've been little more than a footnote in the history books.

The movie that practically defined decopunk is Sky Captain and The World of Tomorrow. Check it out. It might give you some ideas.

 

Adela - Here's a passage I found when looking into Trans-Atlantic flights that might be of use to you.

The North Atlantic presented major challenges for aviators due to unpredictable weather and the huge distances involved coupled with the lack of intermediate stopping points. Initial commercial forays into transatlantic services, therefore, focused more on the South Atlantic, where a number of French, German, and Italian airlines offered seaplane service for mail between South America and West Africa in the 1930s. German airlines, such as Deutsche Luft Hansa, experimented with a number of mail routes over the North Atlantic in the early 1930s, both with seaplanes and with dirigibles, but these were not regularly scheduled services and never led to commercial operations. There were, however, hundreds of transatlantic crossings with passengers made by zeppelins during the late 1920s and 1930s, including probably the most famous zeppelin of all, the luxurious Graf Zeppelin.

Other airlines such as the British Imperial Airways and Pan American Airways began working toward experimental transatlantic flights only in 1936, partly because the British were unwilling to grant landing rights for American air carriers until then. Both airlines decided to use flying boats because concrete runways were rare at coastal airports on the Atlantic, and also because landplanes capable of flying such distances without refueling simply did not exist at the time. Both airlines carried mail rather than passengers in the early years. An average flight from coast to coast, using the Short S.23 Empire flying boats, took nearly a day.

- From the https://www.centennialofflight.net site.

 

If you are doing alternate history, have you looked at the impact of the Great Depression on aviation? If you have no Great Depression, no WWII, it's possible aviation may have advanced to the point of trans-Atlantic flight by the time your story is set. Or, the zeppelins are an awesome way to show that your setting isn't just normal history. I'm sure a lot of people don't know when trans-Atlantic flights would have been feasible for your characters or not. I know whenever I read a story with a zeppelin I am automatically put into an alternate history mindset and willing to have a greater suspension of disbelief for any historical differences.