Intiative will be affected, but AC will not.
Reading the sections on both of these, they do not mention exceptions for negative DEX.
Proficiency Bonus is not added to damage rolls.
Proficiency bonus is added to attack rolls, ability checks, and saving throws for which you are proficient. Damage rolls will add the appropriate modifier for the stat which was used to make the attack. However many spells, especially cantrips, do not add your casting mod to the damage.
There are some class abilities that allow proficiency to be added to damage rolls, but those are a specific exception rather than the general rule.
Firebolt requires you roll 1d20+INT+proficiency vs. AC and deals 1d10 damage
Make a ranged spell attack against the target. On a hit, the target takes 1d10 fire damage. A flammable object hit by this spell ignites if it isn't being
worn or carried. - PHB p. 242
“Spell attack” = roll a d20 and add prof and mod. Spell save means target rolls defense.
Each spell's description indicates whether you need to make an attack roll, or the target needs to make a saving throw, or both.
Saving Throws
Many spells specify that a target can make a saving throw to avoid some or all of a spell’s effects. The spell specifies the ability that the target uses for the save and what happens on a success or failure. The DC to resist one of your spells equals 8 + your spellcasting ability modifier + your proficiency bonus + any special modifiers.
Attack Rolls
Some spells require the caster to make an attack roll to determine whether the spell effect hits the intended target. Your attack bonus with a spell attack equals your spellcasting ability modifier + your proficiency bonus. Most spells that require attack rolls involve ranged attacks. Remember that you have disadvantage on a ranged attack roll if you are within 5 feet of a hostile
creature that can see you and that isn’t incapacitated (see chapter 9). - PHB p. 205
There are two types of attack spells requiring d20 rolls: melee attack spells and ranged attack spells.
The difference is that melee attack spells will not be made at disadvantage when next to an enemy combatant whereas ranged spells would be (and all ranged attacks for that matter).
Best Answer
No. Ranged weapon attacks use Dexterity as their ability modifier. When you cast a spell that requires an attack roll (note: most don't) you're not making a weapon attack.
PHB page 194, Attack Rolls > Modifiers to the roll > Ability Modifier:
PHB page 205, Attack Rolls:
Long story short: as a Cleric your cleric spells with attack rolls will add your Wisdom mod bonus, not your Dexterity bonus, regardless of whether they are ranged spell attacks or melee spell attacks.
Separately, if your Cleric were to take the Mage Initiate feat to gain access to spells from the spell lists of other classes, you would have to use that class's spellcasting ability modifier.