Well done for choosing phpBB3!
Quick observation…
I noticed that the registration form does not require the answering of a CAPTCHA test… now as I understand it moderators approve the first two posts of a user to prevent spam, CAPTCHA will reduce that workload…
Best,
Jethro.
No it won’t 
.
We are using a system that checks new registrations, profile changes and new posts against various blacklist services. That is significantly more effective than captchas because practically all captchas are broken.
Before introducing the blacklist system, we used captchas and had 50+ spammer registrations per day. Now we had about 25 in 6 weeks.