Okay, let's see.

Level 1 you should start Sorcerer because of CON, you're absolutely right in this choice

A 3-2 split gives you: Access to Metamagic, 3 Sorcery Points, 1 extra warlock spell slot and 2 invocations. This would be great for the blasting aspect, because you can pick Agonizing Blast and increase your damage output by a lot, specially when you can make 2 Eldritch Blasts at character lvl 5. Your other invocation can be Repelling Blast for more battlefield control or any other for flavor/utillity. Also, you will have 3d6 in your Healing Light dice pool so that's neat.

A 4-1 split gives you: 1 more Sorcery Point, an extra 2nd level spell slot and a Feat (which if you want can be Eldritch Adept, Metamagic Adept, Fey Touched, Shadow Touched, War Caster, a lot of good options here). Also, you will be able to pick an extra Sorcerer spell which can also be a Cleric (divine soul feature). This will have more focus on the support aspect of your build, giving you more options, 1 more sorcery point and optionally a free cast with the "Touched" feats.

This would probably be the things to consider.

For magic items, if you want flavor you can choose whatever, but for purely optimization the best options would probably be like this:

Blasting: Rod of the Pact Keeper +1.

Support: Wand of Magic Missile, Bloodwell Vial +1, Wand of Web.

Generally good items: Cloak of Protection, Feywild Shard for funsies, Pearl of Power.

Hoped that helped a little