There are plenty of free services you can leverage.
Community TS3: contact [WiE] Phelan Kell to get setup. Designated unit leaders have the ability to create channel rooms, set password protection, and kick/ban unwanted users from their channel
Forum hosting: Several of our clans/units use
www.enjin.com for their hosting needs. The 12th uses
http://www.freeforums.org/ Both are have free versions.
Once you have that stuff setup, like the other guys said, jump in with both feet! Challenge other units, most of the times the community can find a server to do the hosting if they don't have control of one. I know when the 12th first started I only challenged the larger units that could host are matches so it wouldn't be an issue.
Beyond that, I'd say the biggest challenge is maintaining interest and momentum.
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I also wanted to add that having a "mentor" unit really helps when starting out. The Dragoons really helped us a lot when we first started. Showed us the ins and outs of hosting matching, how to plan for "league style" drops, and even invited us to one of their big events
