Me and Owl already looked into minigames and servers that have minigames. Would not recommend having minigames for more than an event (especially hg/sg as it is not as popular compared to newer gamemodes).
The biggest issue is population. Low population can create boring and slow gameplay that minigames is not meant to have. Not only that, you need enough players that are willing to play the same gamemode. If we look at the recent hunger games event xG held, with 10-20 players, anyone who died early found themselves sitting in a waiting room for 5 to 10+ minutes. That is not very fun at all considering you don't have anything meaningful to do in game during the hang time. The large minigame servers have a big enough population to allow players to get into a new game within seconds. There's a reason there is only two big minigame servers.
Other than that you have to worry about the following:
Plugin configuration and compatibility.
Lack of uniqueness from out-of-the-box gamemode plugins.
Anti-cheat
Teaming in solo gamemodes (and all of the loopholing people will pull).
Incentive to play on the server (this applies to every type of server, but some more so than others).
Factions/Townie would be the way to go with the current foundation. However, the gamemode chosen should be the sole focus until the server is operational.