What do you need?
First decide on your budget.
A great starting point is an audio interface.
The Scarlet 214i and other products is an excellent choice but there are many to chose from.
Good monitor speakers are also a great investment. The rocket’s are good although can tend to be quite bassy. The yamaha speakers are good representation of recorded sound.
A keyboard is an essential for any music producer and basic keyboard skills are helpful in music composition. The Novation series are very good products and keyboard size differ from 25, 49, and 65 keys depending on how much space you have.
Also with the novation they tend to map instantly to most of popular music production software.
How do i connect them?
Most use USB connections.
Most essential Element
Software is key.
There are a number of different programs including logic, Ableton, Reason, Cubase, and more. The important thing is to become familiar with one of them and most will map to the keyboard and you can manually map them.