FrogReaver
The most respectful and polite poster ever
I think I'd want eldritch blast as the attack, just like the fighter has his sword. Save the spells for healing or other utility. If the spells known are attacks then they will be used in combat rather than the healing ones. Keeping eldritch blast as the attack option keeps it straightforward on choices for resource management and strategy and allows them to be the healer. If you take attack spells you become a little more effective at attacks sometimes but you give up using your limited slot for healing or utility to do so and make it a tougher judgment call on what to do in various situations.
I get that but I personally wouldn't use the celestial warlock here. More likely the fiend as it's a more familiar trope.
I actually think avoiding all but 1-2 utility spells is the way to go. I don't think warlocks get enough healing spells to go with 1-2 utility spells to make up their list.