I went to Warsaw last November. It was a lot of fun and while a bit cold, nothing worse than New England in late fall. Transportation in the city is very good and many of the sites are within walking distances. Bring a smart phone with a good direction application.
The Warsaw Uprising museum is a must see, though I thought the lighting in the museum made it challenging at times to read the displays (in English and Polish). This may be the intent of the museum but it made it hard on my 60+ year old eyes. The sewer exhibit was my favorite part.
The Polish Army museum looked REALLY good on the website and at the new building . . . BUT all three times I went to visit it was closed (for technical reasons!). Drat. Hopefully it will be open for your visit.
The citadel north of the city is the home of the New Polish Army Museum and the Museum of Polish history. The latter is also very nice but not well populated with exhibits. It may have more by the time you go. The citadel itself is a good example of mid 19th century fortifications and similar to what you might see in the US at several locations. Interesting to walk around and compare and contrast.
The Katyn Museum is also in the citadel. It only has Polish language displays and is very depressing as one might imagine. Worth the look.
I went to the hobby shop as I wandered around the city (and got lost several times). It was neat to see how a different country organized their stuff. The shop owners knew English so there was no trouble there.
The Tomb of the Unknow Soldier was also of interest to see. Very accessible and compelling. Much of Polish military history in the last hundred years is a bit somber. This is no different.
The old city has some fortifications of note, but also many museums and palaces of the old monarchy. It was leveled in the Second World War but rebuilt in the 1970s by the communist government.
Many statues in the main avenues of historical figures, some of which you may recognize. The city has a French architectural style to my highly untrained eyes.
Enjoy your time. Enjoy the vodka and kartacze (potato dumplings).