Interesting take on a tempest cleric build. I like that you highlighted ways the character will play differently as they level up. One question on the ability scores:
You never said what the Dex will be, but I am assuming 16 since you later mention a +3 dex mod? Beginning stats are 8/16/14/10/16/8? If that's the case, I think you are putting too much into Dex considering that you are wearing scale mail and giving up on the longbow after just one level. I'd suggest starting with Dex 13 + 1 from V. human and put the extra 4 points somewhere else, maybe 10 Str and 10 Cha or even just 12 Cha since Cha is a proficient save. Maybe put 2 points into Con to start with an odd score in case you wanted to take the Resilient (Con) feat down the line.
[Edit: yes you'll still need Dex for that rapier, but IME the weapon attacks become a lot less important as you head into Tier 2]
Spell selection isn't that important since you can change them out every day, but early on, when you only have 2-3 spell slots, I would focus on spells that you know will work when you need them to work, instead of spells that require a successful attack roll. After personal experience missing too many Guiding Bolts, I limit the all-or-nothing damage spells to cantrips. If I'm going to burn one of only two daily spell slots, I need to have something to show for it.
