I have added all the above proficiencies :)

I don't really have any specific Celestial in mind…

I have some ideas on the sort of attitude it would have, so if you can think of anything that fits…
Probably something Neutral Good
Otherwise, happy with whatever you might think is suitable.

Patrons Attitudes: Just some thoughts otherwise, below is similar to No.3 in XGtE.

• Wants a champion to continue its crusade against evil
• Can only make a pact and communicate directly with someone who has the amulet
• Disappointed that the first person to find amulet in hundreds of years wasn’t more ‘heroic’, but is determined to make you a great hero and continue its crusade anyway.
• Has certain ideas about how a champion against evil should behave, thought does not enforce this other than harsh admonishment.
• For the short term, is unconcerned with how you spend your time so long are you are honing your skills and championing the cause of good.

Special Terms: When you use an eldritch invocation, you must speak your patrons name aloud or risk incurring its displeasure. If possible, change this from “risk incurring its displeasure”, to “it ignores you and does not allow you to use the invocation” (mostly if I feel the party gets too annoyed with me invoking my patrons name every time I cast eldritch blast)
Binding Mark: Your nose glows in the dark

Would it be possible to exchange Resistance for Shillelagh?

For Guild Merchant I will take proficiency with Oared Vehicles (I assume I need this to use a barge effectively), and a small barge.

For Halfling, I’ll go Animal Handling (assuming I get persuasion as part of the guild merchant package).

For Warlock, Proficiencies are: Deception and Arcana.
Weapon Proficiencies: Short Blades, Clubs & Staffs, Thrown & Slings, Nets & Chains.

Yeah, I like the second one, simple, nice medallion, and very merchanty.

https://www.artstation.com/artwork/d-d-s-regis-the-halfling

https://www.google.com/imgres?imgurl=http://i.imgur.com/NWGhml4.jpg&imgrefurl=http://www.giantitp.com/forums/showthread.php?485736-Selling-your-Soul-at-a-Premium-The-Warlock-s-Guide-to-Power&tbnid=Wye12xZuLWfU9M&vet=1&docid=dUrbS3NMN_LrvM&w=488&h=736&q=halfling+warlock+breath+fire&source=sh/x/im

I guess it might be a little darker than you'd want though… but it does have an amulet =P

I do have some preferences, but I’ll go with whatever you find if too hard.

• Mid 20s to 30s
• Lighter coloured clothes
• Finesse weapons
• Still want to go with the gold medallion idea for arcane focus.

Also, you can start with a small barge of your own in place of artisan's tools. That would be cool.

Your choice.

Halfling. for your Weak flaw you get one of following: Acrobatics, Animal handling, Persuasion, Stealth, Thrown & Slings (Simple), any 1 vehicle (or vehicle group if using our grouped proficiency house rule).

Warlock. See the Warlock page over at CC.

The halfling write up here on this site under Major Races does mention that a lot of family names have to do with river life, but you don't have to. have you read the entry for halflings for Elsir Vale? Might help with some of this. Personality especially - after the mephit within you ;)

As far as background, decided to go with Merchant/Trader, very in line with light foot halflings in the setting.

This is what I was thinking, this will be my usual long thought train.

Eddie comes from a merchant clan who trades across the veil and beyond (no fixed location, though clan members could be found in various places if necessary).
As is tradition for the clan, when children come of age, they are given some capital and set off to build their own businesses. In this way, they test and prove their abilities. Most eventually return to the clan, bringing in new stock, trade routes, skills and other opportunities. This allows the clan business to expand and diversify.

After a period as an apprentice under his uncle (children are preferred to be apprenticed under someone other than their parents), Eddie was given a small amount of gold and set off to establish himself in Brindol and surrounds.
Having a keen interest in weird and interesting artefacts and other items, Eddie set himself up as an import/exporter of strange items and artefacts, of middling success.

Eddie enjoys the work, but his desire to do well is more due to family expectation, than any particular ambition.
At heart, Eddie is family focused, and feels he can do better before returning to the family fold.

At some point, while looking to acquire some new stock, Eddie found himself in a dangerous situation. Pleading for help, Eddie found it from an unexpected source.
One of the items he was looking to acquire for stock, An old amulet, dusty gold with a crystal in the centre, and strange symbols circling it, spoke to him, offering him power and survival in exchange for service.
Feeling he had no option, Eddie took the deal, and entered the service of his Patron, who communicates with him directly through the amulet, which also serves as an arcane focus.
In exchange for his surviving, Eddie was, reluctantly, made to take up his Patron’s crusade against the forces of darkness, and, at his urging, joined up with the Watchers in order to do so.

• Eldritch Blast
• Mage Hand

Other Spells - Going All In on the expanded Celestial spell list;

• Cure Wounds (1)
• Guiding Bolt (1)
• Flaming Sphere (2)
• Lesser Restoration (2)

Pact Boon: Pact of the Tomb
Bonus Cantrips

• Spare the Dying
• Resistance
• Guidance

Invocations

• Agonising Blast
• Armor of Shadows

It could even be a good creature of the world like a unicorn, ki-rin, good dragon, etc.

Basically, any force of good. :)

2 cantrips
4 spells (up to 2 can be 2nd level; rest are 1st)
Our Spells Page lists all available spells and cantrips for you.

2 invocations
Your pact boon
Our Warlock page lists sources other than PHB where you can find invocations and pact boons.

If you prefer to be a stout (+1 CON) just let me know ;)

I will do everything randomly unless you tell me some specific things you want, like:

Background
Skills
Weapon groups
Any extra Drawbacks?
Racial feats/Feats

etc.