First of all you need at least 30gigs free on your sdcard.
Second you need at least 5gigs free on your system nand memory (save files)
Thirdly, you can NOT access the MyCareer mode, unless you turn off stealth mode and have connect to the internet, it requires an online account from 2k games, not sure if it needs an nintendo online as well, but it does require online connection, before MyCareer option works.