Single cat/ Late kitty introduction success stories?

My boyfriend and I are planning on receiving a Siberian kitten in about 6 months. We are treating it like I'm pregnant with a human baby. Catification, nesting, watching nothing but Jackson Galaxy videos online (I plan to play with my cat EVERY SINGLE DAY, ok??)

I recently noticed that a lot of people suggest adopting 2 kittens right away. My boyfriend and I live in a 970 sq ft apartment and he is pretty set on adopting one to start out with, seeing how our finances change and whether we move into a bigger place, and considering getting a second cat in about a year.

I also really want to start with one cat, honestly, because this is my first time having a pet. But the internet (and my intense step mom) has essentially told me that if we have just one cat, it will grow up to have terrible separation anxiety, behavioral issues, and never bond to a future cat.

I am just wondering what your experiences having a single cat have been, or if you introduced a second kitten later on, how it went and what advice you have?

I really want to do a good job for our future pet. Please let me know what your thoughts are. Thank you guys <3