[Marco van Herwaarden]

I would do it slightly different:
1) Install vB3
2) Do a test conversion to testboard
3) Apply Styles (skins) and modifications on testboard
4) Test
5) test
6) export Styles from testboard
7) setup Production baord
8) Close phpBB and export
9) Import into production
10) Test
11) Import style from testboard (could also be done before)
12) Make full backup (database and filesystem)
13) Copy over modified files from testboard, run installers from hacks on production, add phrases/settings if needed
14) Test
15) Start second full backup and keep testing
16) Test
17) Open board and tell a few members/moderators
18) Open for public