Does buying members work?
No. Fake members don't chat, they drive away active members and they're against Discord's rules.
How many channels should there be?
Few at first: general chat, announcements, rules, role picking and one or two topic channels. Open channels as the need arises.
Should I do partnerships?
Yes, with servers that have a similar audience. You can collect partnership requests with an application form.
Which bots are a must?
A single multi-purpose bot is enough for most servers; multiple bots doing the same job create double messages and confusion.