WMA files are a proprietary Microsoft format, and
AFAIK won't play on an iPad. I believe you can convert them to an Apple compatible format in iTunes on your Windows machine. Apple distributes its files in AAC, which is NOT an Apple proprietary format, and is now quite widely used. iTunes will also happily play MP3s.
Assuming your WMA files are WMA lossy (if you don't recognize what I'm talking about, they are lossy) it's really not a good idea to try to reduce the size, as you lose quality going from one lossy format to another. I'm old af, and I find 128kbps quite satisfactory, but 128 kbps files made from a different sort of 128 might cause me occasional annoyance.
IME the iPad is great for web browsing, looking at photographs, and especially for reading documents. An app called GoodReader will enable you to have with you at all times PDFs of Pilot's Notes of every type you can imagine, plus service manuals for all the fine products of St Pratt and St Whitney. But the iPad is definitely not a laptop replacement.
Good luck.