If you want to use a standard-type stand you can't really go above 27"-28" in a 16:9. 32" would just barely fit and you would likely have to get your own mount as the included stand will be too tall. Ultrawide is probably the way to go if you want bigger, but those seem to start at $500 for 1440p unless you go Korean.
I would think twice about 144 Hz at this budget for an MMO. If it's not competitive PVP you won't be doing super fast camera swivels much, and many MMOs end up CPU-bound anyway. Adaptive sync can help smooth over CPU sluggishness but you are usually back to looking at wide ranges to get something useful there.
WoW text/UI does scale pretty nice at 4K and its not that demanding a game, so I would also consider that even if its a 60 hz panel. These days word and web browsers work well with windows DPI and you can enjoy sharp easy to read text. There are many big brand name choices at 27-28" in your price bracket (Dell, LG, Acer, Viewsonic, Samsung, whoever), just be sure to get an IPS one as there are some TNs running around.