Personally, I don't concern myself with what members are active. I've had members that were lurkers, and contributed more as they seen the community grow.
I try to make at least 1 thread per day on my forum. I do go days without creating new discussions, but I'm always responding to topics when I can add value, and interact with my members.
I like to have a good balance of topics started by more than just me on my forum.
Usually members will follow where the admins are active, so if you post a lot content in your main sections, your members will likely do the same. I typically ignore the off topic part of my forum.
I joined admin forums, post exchanges, and promoted all over social media. I filled my forums with content, and I continue to post content regularly on my forums.
It varies I've had days where I did promotions and we had 7-8 members join within 24 hours on my forum, it's been taking a month to go from 175 members to 200(198 members ATM). Slowly getting bigger.
What's your thoughts on forums with a big staff team? How many staff members does your forum have?
My forum currently only has 3 staff members including myself. I don't plan on adding to the team, until we get bigger.
Most/all addons for Xenforo are paid plugins since the software is for users with a paid license. There are plenty of open source forum softwares with addons that may suit your needs. SMF would be a good choice, if you're looking for a free solution.
I have a few domains I've been sitting on that I'm not using, but I do plan to eventually get around into developing them. I don't buy domains unless I plan on building sites for them.
The more you post your links the better. I don't do it for big traffic, but every little bit of traffic helps. Also when you link your site on more sites with do follow links it helps you get more of a boost in search engines, and get more traffic from SEO.