I have the 8GB SQ1 256GB Surface Pro X since about a year now. I'd say for your use-case, get the SPX. Mine is similar to yours, except I dont open 10-20 tabs in my browser, but I use more OneNote, Excel and Word. It works a treat and I love my SPX (it's my daily driver). Trust me, once you put a SIM card in there and enjoy the LTE anywhere, it's hard to go back to a non-LTE device. Totally worth it! Alongside the fact that it is thinner, lighter and has smaller bezels than the SP7.

Mine's a Maxis SIM. Duplicated from my main line to be data-only. Not sure if that makes a difference, but from what other people have said even normal SIMs with data + mobile line should work.