I cycled across Poland 3 times. Kostrzyn - various routes to Suwalki/Sejny. Bike/trains every time, boarding trains in cities and small villages.
Language isn't a massive problem because many young people speak English or German. You probably won't get into deep conversations but you will be able to ask the route/buy food etc. Of couse it's always better to know at least few words in Polish because that will make locals incredibly friendly. But don't worry!
You can board any train anywhere with your bike but I'm talking about normal bicycle.

Don't know their attitude to trikes though that probably will be your advantage because it's so exotic.
Most of the trains will require you to buy one ticket for you and one for your bike. Bike ticket cost a bit less than a ticket for you. Anyway, train tickets in Poland are cheap.
Roads in Poland are OK. In some places you may find yourself in the middle of nowhere but the tarmac will be new and of perfect quality. Beware - you also can appear on the road that looks like 2 World War ended just yesterday (don't ask me how I know this

) and it's easier to push your bike instead of trying to ride it.
Cycling on motorways (E roads on Google maps) is forbidden. Some A roads also don't want to see a cyclist using them. I also recommend to check which roads are motorways because Polish are constantly building new roads (like a new motorway near Bydgoszcz in 2019 and it's probably already built).
Main roads are super busy but many of them have got very wide hard shoulder. This has to be checked on Google maps.
I would advise to use small country roads because they are almost traffic free. Car drivers are ok in my experience - they will give you a wide berth when overtaking you.
Also don't be surprised to face unpaved road. For me it was quite fun to cycle on them after a constant tarmac.
Prepare yourself for lose dogs. And they are not friendly - if they catch you they will bite you. Always have a knife easy to access or pepper spray.
Poland roads have got petrol stations every 15 - 20 miles so don't bother yourself with bags of food and drinks. Orlen petrol stations sell nice hot dogs/ice cream/coffee etc. If you will cycle on tiny country lanes then every tiniest village has got a shop (sklep in Polish, you're welcome).
Also you may meet some unfriendly people. Angry drivers. Dogs. Crap roads. Grumpy cashier at the till. Whatever. These things also add up to the adventure.