First off, I wasn't trying to bash you. The "monstrously incompetent" referred to the build you presented, as a 7th level tank, not to yourself!
That said, the problem with your build is that while it'll be quite alright at the later levels, right now is when you need to survive 13.67 level-appropriate encounters to see next level. 2nd level spells, BAB +3, light armor, and 30-something HP are not going to cut it there.
Now clerics can be surprisingly effective tanks. But they become so by using their spellcasting ability along with divine/devotion feats, on top of a strong chassis (OK HP, BAB, good saves, good armor prof etc.). Taking Lumi as a race is problematic here: the Lumi's upsides don't warrant its downsides in a full caster build, unless you're starting at very high levels.
You need all the tools at your disposal to be able to do your tanking job, and you need them now. A tank will, by definition, be in the thick of things, so waiting for the good stuff to happen at later levels is not a good survival strategy. Divine Power, for instance, is a must-have if you're going to melee a lot - you won't be able to keep up with the Big Stupid Fighter otherwise. You can have Divine Power at 7th level, but not if you take a level adjusted race.
Similarly, your best buffs will need to be either kept up all day (Divine Metamagic:Persist), or be available at a moment's notice (Divine Metamagic: Quicken). Otherwise you lose precious rounds buffing while your teammates are getting hacked up. However, a Lumi Cloistered Cleric 3 has only two open feats (your sample build includes two feats at level 1, which is likely an error), which all but precludes DMM. I guess you can take the Planning Domain and pull off DMM (Persist), but now you don't even have Power Attack yet, and possibly not enough turning attempts anyway.
So if your party needs a tank now, consider a regular Human (Lesser Aasimar is a good alternative if it's allowed) Cleric 7: you'll have 4th level spells (Divine Power is online, but you also get Freedom of Movement should you need it, Dispel Magic to take the fight out of Mr. BigBadEvilAndPrebuffedGuy etc.), you'll have 6d8 + 7xCon + 8 HP (assuming Con 14, that's 49 HP), BAB +5 unbuffed, and you'll have the best heavy armor available (and at this level that still counts for something). You also have two more open feats to spend on useful stuff like Power Attack and Extra Turning, making your DMM'd self buffs that much better.
