Should I upgrade my phono linestage first or the tonearm for better results?

The main advantage from the Graham Arm is its own cartridge adjuster. The user can align a cartridge spot on and I think, that is one reason why Graham Arms sound better than others.
A new, expensive  Arm with wrong calibration is useless.

+1 on the Graham arms, they are exceedingly easy to set up with the "in arm" included protractor and the "underside up" cartridge installation jig.

Good Listening


Peter

I had the Acoustech PH1-P with the Virtuoso 2 cartridge. The PH1-P is a nice sounding phono stage, better than others that I tried in the sub $1k price range, but it can be improved upon. 

In changing from the PH1-P to a better phono stage in the $2k-$3.5k range (I tried several in this price range), I experienced more of a holographic, natural sounding soundstage. Vocals were much improved. Clicks and pops were reduced. Dynamics were better.

Going from the Virtuoso 2 to a Benz Silver Reference MC cartidge brought a very noticeable improvement in background noise, and a more natural, relaxed, 3D, feeling presentation.

I now own an Allnic H-3000 phono stage, which is more than you want to spend. I bring this up because I can use an inexpensive Technics SL-5300 turntable with its built in arm, with an inexpensive Denon MC cartridge, and get great sound out of this combination. This demonstrates to me that a very good phono stage is worth the investment, and has had the most impact in my analog set up. 

Your tonearm by most accounts is very good. I would upgrade the phono stage and cartridge first.

My opinion is very biased (admittedly) but there it goes anyway - I always think that improvements to phono stages are more worthwhile than tonearm changes. I'm a die-hard Graham fan, though I intensely dislike Clearaudio cartridges. They are one of the current fads regarding cartridge brands, but I feel sorry to disappoint you, I don't enjoy the "German" school when it comes to cartridges and IMHO they are amusical devices. 
Though "colored" (in a very good way however), I'd stick to a Koetsu, I've never seen anything as musical. The loading can be very strange and very few phono stages will do it, i.e., 10 ohms (yes!) and quite odd pF values, but then I think it is worth every effort. The Koetsu gets out of the way and leaves you with pure music, extracting the best out of even old recordings! The Clearaudio is, to me, an analytic tool, albeit a lifeless one which will not stir my emotions,