Welcome bokally to the forums.

This is a very hard question to answer without knowing what exactly you wish to do with BiaB (Band-in-a-Box) and RB (RealBand). Are you a vocalist, keyboardist, guitarist? How accomplished of a musician are you? Hobbyist, Pro or somewhere in-between? What are your final goals for your home studio? What type of computer do you have? What kind of soundcard does it have? How much of a computer geek are you? Things like this are important.

Assuming you are just starting out with computer generated music I would suggest buying just two items. Monitors like jazzmandan suggested and a small mixer like a this Behringer mixer The mixer is especially useful if you are going to sing, play guitar and or keyboard into your computer. Then I would learn BiaB and RB.

After you become efficient with them then you may want to add on to your studio with things like a midi controller (keyboard, guitar and/or wind), better sound card, monitors and soundsources like Kontakt or hard synths if you use midi a lot.

There are a number of ways to go depending on your needs and skill levels.

I hope this helps – good luck.

Ps – you will find this forum one of the best on the internet. Everyone here is very helpful and some are extremely knowledgeable. The only stupid question is one that is not asked.

OK, a random thought;
Why does toilet paper need a commercial? Who's not buying it?

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware