Mac Pro - Customization Question

Hi all,

I am considering purchasing a Mac Pro in the not too distant future and I am curious about how customizable the Mac Pro is after purchasing.

My budget is pushed by going for the powerful Mac Pro so I'm looking for advice on what I should add / spend my money on in the initial purchase and suggestions on what I should then add/purchase the third party vendor route.

For example, I know RAM is notoriously expensive through Apple and I am comfortable adding it myself so I am looking for recommendations along the lines of, 'go ahead and purchase X amount of RAM now with this capacity so you can purchase X amount later to maximize / scale the RAM to capacity later through third party content'.

Also, I am a graphic designer who typically hast 7-10 programs at once with 20 tabs open in Chrome so any suggestions on where I can achieve optimal performance in the graphics card etc and/or processing speed would be wonderful.

Essentially, I am looking to max out the skeleton of the Mac Pro at the least expensive cost while being able to build / add into it once it's been purchased.

Thanks for any suggestions in advance