I’ve just started an Eberron campaign as a Guild Artisan Mark of Healing Halfling Rogue, with the character concept I have going MC Warlock (Hexblade). The character is a House Jorasco healer who has been lent to the Boromar Clan as part of the agreement they have, so is the soft support and face for the group (Gnome Articifer, Shifter Barbarian, Tabaxi Rogue).

DM let us roll stats and I rolled very high: 16, 16, 16, 15 15, 13. Each party member was allowed to take an uncommon magic item at creation, but part of my concept was that my rogue had worked in a joint Jorasco/Valadis medical research facility in the Mror Holds experimenting with Symbionts. In exchange for a 16 becoming a 9 and a 15 becoming an 8, I was allowed by the DM to take Dyrrn’s Tenticle Whip as my magic item. The whip will be my Hex Weapon and will talk to my character subconsciously as her patron.

After racial bonuses, my stats are 8 / 18 / 13 / 9 / 16 / 16, skill prof. in Deception, Insight, Medicine, Perception (expertise), Persuasion (expertise), and Stealth.

For Combat, planning to use the whip in Melee for sneak attacks and with Booming Blade, then Eldritch Blasts at Range. Hexblade’s curse and Hex as bonus actions. Thinking Swashbuckler but open to suggestions! Also, should I go Med. Armor and/or Shield?

I haven’t played as a warlock before and am looking for ideas about cantrips/spells that work well for a Rogue MC as well as being thematic for a character with a Symbiont/Daelkyr patron. And strategic suggestions? Specifically what order would you Level in? Was thinking Rogue 1 / Warlock 3 / Rogue 3 (use ASI on CHA) / War 1 (use ASI on CHA to get it to 20 and use it for my whip attacks over Dex). Also, what pact would work well? Leaning towards Tome to give some additions cantrips and spells.

Tome Pact Warlocks with Hexblade Patrons can be very versatile and great fun. As a Rogue, you expect your melee damage to come from Sneak Attack; an owl familiar can give you advantage on one attack per round with little risk of dying (flyby trait).

IMO the best Rogue/Warlock split is 12 Rogue / 8 Warlock if you want to be mostly Rogue, or 12 Warlock / 8 Rogue if you want to be mostly Warlock.

Do the levels in the order that makes sense for your character, but it's nice to get a level or two of Warlock while you're still a tier 1 character, since your Cantrips scale with overall character level.

Thanks for the reply! Really good points, do you recommend Pact of the Tome over Chain to get the familiar? 

And yes, plan to grab my Warlock levels early, as they seem to be weighted high for low tiers. 

Any suggestions on using Light vs. Medium Armor? Any issues with using a shield? Would mean I couldn’t attack with my off-hand, but looking at being in melee but using the reach property of the whip as much as possible. 

I've never played Chain pact, so I can't comment based on experience. I've done some Blade, and I find that I love Tome for the versatility.

I always try to get a breastplate (medium without stealth penalty) and shield, although as a Rogue MC I'd probably drop the shield once I get Swashbuckler abilities - I'd likely dual wield from there on:

1. Close half my movement.
2. Booming Blade with short sword (and Sneak Attack damage)(Owl for advantage).
3. Bonus action second attack with offhand short sword - especially if first attack missed.
4. Retreat half my movement without AOO due to Fancy Footwork.
5. If they pursue me, they get the secondary Booming Blade damage.