Need help making a Moon Druid/Primeval Guardian

My current character is a level 5 druid/ level 1 ranger. I initially started the game as a coastal land druid. I took the level of ranger in an attempt to make my character a little more beefy and to make him more capable in combat. However, after discussing my lack of combat ability, my DM allowed me to respec as a circle of the moon druid. I felt like I should keep my ranger level, if nothing else for the the flavor of it. My plan was to continue running with 1 ranger level, until I saw the ranger UA and fell in love with the concept of the Primeval Guardian. I feel like it fits really well thematically with a druid/ranger multiclass. I'm not a min/maxer, but if I go with this build I would at least like to make it viable. We'll probably be playing these character until level 10-11 (CoS). So my question is, how can I make this a useful viable option? When I'm in humanoid form casting spells, I will often pick a spot and stay in it, using my move action to dodge. Because of that, the loss of move speed in guardian form wouldn't be detrimental to me. I was thinking a good way to add a little kick to this would be with Shillelagh, Polearm Master feat, and Tunnel Fighter style. Plan would be to stay in one place and cast, will getting multiple AoO on anything that entered by 15 ft. range. If anyone has any other ways I could work this build or any advice, it would be much appreciated!!