Help with upgrading my rig

[noodles_lover]

So, i'm upgrading my rig and kind of in a budget. I plan on going for :

• * Ryzen 5 1600
  * ASRock - AB350M
  * Kingston - A400 240GB SSD
  * Radeon R9 280X 3GB
  * Cooler Master - VSM 650W
  * Seagate 7200 1TB HDD

I already have the PSU,HDD and the GPU , which i don't plan on changing now. My concerns are : Should i go for 1x8GB Stick (SingleChannel) or 2x4GB (DualChannel) ?
I'm worried about the next upgrade, because the MoBo has only 2 slots. Is it worth going DualChannel for now but in the future swapping 1x4gb for 1x8gb = 12GB , instead of going 1x8GB single now and later going for 2x8GB dual ?
Oh - Are RAM frequencies really game-changing? I plan on going 2133 , because higher frqcs are really expensive in my country.
Last thing - I think i can go for 240GB SSD, but i would like to go for something cheaper (120GB) if i could. Is 240GB a must-go or can 120GB hold it?
Also, please, i'm doing everything the cheapest i can, so i don't plan on going for another mobo or processor.
 Computer will be used for gaming / photoshop / lightroom. Thank you upfront!

[patio]

Toldya earlier ...for dual channel RAM's need to match...

As to the SSD a 120 is a waste of money...it'll be full in no time...

[patio]

PS...photoshop and budget PC is a crapshoot...yer choice.

[Mark.]

@noodles,
to give you some idea, my 120GB SSD has 52GB used.
that's just Windows 10, Office 2016, Acrobat, iTunes (just to name the big boys) - no games.

breakdown of folders is Windows - 18GB, Program Files - 11GB, Users - 3GB, and my personal files - 21GB

you want to add some whoppers like Photoshop, Lightroom and games so 120GB is getting tight without too much effort.

then consider reserving 10% of the SSD space for over-provisioning and the 250GB size is looking attractive right from the get-go.

[patio]

+1