1. key Alt+1
2. key Alt+j, then 0, then 1
3. key F5 ^*
4. key F6 ^*
5. key Ctrl+p ^*
6. key Ctrl+n ^*
7. key Alt+Left ^*
8. key Alt+Right ^*
9. key Alt+Up ^*
10. key Alt+Down ^*
11. key Alt+a (if buffer #1 is first in hotlist)
12. left mouse button with long gesture to the left (with mouse enabled)
13. command /buffer 1
14. command /buffer core.weechat (if core buffer is #1)
15. command /buffer close 2-99999 (joke! - this will destroy all buffers and keep only buffer(s) with number 1)
16. command /buffer move 1 (joke! - current buffer will become #1)

There are other ways with scripts, but it's cheating!

^* : press key many times until you reach buffer #1.