Opinions on a half orc champion warlock

[LeonBH]

I can see this working. If you go Champion 5/Warlock 3, you get access to Shadow Blade, giving you a 2d8 light, finesse weapon that you roll at advantage with under dim light or dark conditions. Due to being a Champion, your Con saves are pretty good, so you won't waste this spell often.

It lets you be SAD if you allow your Charisma to rest at only 13. On top of that, you have an increased crit range. You would be an excellent two weapon fighter (wielding a short sword with your off hand). If you go this path, GWM and PAM will not be your style.

As for the patron, Celestial is good for you. This is because Pact of the Chain synergizes with it well. Select Gift of the Ever Living Ones as your invocation. This maximizes any and all healing you receive (including hit dice and second wind), but it also synergizes well with the Healing Light ability of the Celestial Warlock, which lets you heal 1d6 HP with a bonus action (at level 3, you have a pool of 4d6, and with a 13 Charisma, you can spend 1d6 of this per bonus action; or you can spend 2d6 if you went to 14 Charisma).

This means, if you're in need of healing, you can either take a second wind bonus action to heal up 17 HP (1d12 maximized + fighter level 5) or, if you're done with that, use Healing Light to heal 6 HP (or 12 HP, depending on your Charisma modifier).

You probably won't want to cast any other spell than Shadow Blade, and you'll only have two spell slots to cast from. This means you shouldn't cast any other spell in combat in case you lose concentration. So your other spells should all be utility like Invisibility.