Fantastic Four Forever !

After months of thinking & evaluating multiple parameters like budget, usage, frequency of changing countries, lifestyle etc., I have finally decided to maintain a 4-watch collection. 

The idea is to maintain 4 watches (1 Diver, 1 Dress, 1 Field and 1 GADA) and keep upgrading them. I think it gives me enough flexibility with options, allows me to plan budgets for the watches and also give enough wrist time to all watches that I own. 

I have kind of finalized on my first set of upgrades. My current collection is slightly imbalanced with 2 divers, 1 dress and 1 sort of everyday watch. This is how my current upgradation plan looks 

Current Collection (Attached Image) - 

1. Seiko SKX013 - Diver 
2. Invicta Pro Diver - Diver 
3. Tissot Visodate Heritage - Dress 
4. Swatch Twice Again - Beat/Everyday

Proposed Upgradation (Sample Images Shown)

1.  Citizen Promaster Solar - Diver | Solar | Silicon Strap
2.  Boldr Field Medic II Chrono - Field | Mecha - Quartz | NATO
3. Tissot Visodate Heritage - Dress | Quartz | Leather (Owned)
4.  Lorier Falcon III - GADA | Mechanical | Steel

For the first series of upgradation, I have kept the budget to max 1000 GBP (for 3 watches). I have also tried to balance out the movements and the strap types. 

While the above list is fixed for now, I have kept some scope for flexibility in case I want to fit in a G-Shock, a Tissot PRX or even a Marathon GPQ somewhere. Not sure which one should I let go but :P. The above list looks quite balanced right now. 

But the first step before I start upgrading is to find a way to sell my existing watches at fair prices. I am not sure about the Swatch and the Invicta resale values, but the Seiko SXK013 should have a decent value, I guess.

This is where I need some guidance from fellow crunchers on what's the best way to sell these watches. Whether I should go to brick & mortar shops and sell it for cash or online sources like Chrono24 work well. 

I just want to be assured of getting proper value and also a fair and legitimate transaction without any hassles. 

I am currently based in Manchester, UK and am new to this place. So, want to be extra careful.

Looking forward to suggestions on how to go about this and also what does the group here think about my upgradation plan :) Would love to hear some opinions here.