You could beat the game without paying. One of the biggest things worth buying with death metals is expanding your storage box (so you don't have to pick and choose with resource/mushroom hoarding), though there are quite a few death metals you can receive from quest/login rewards to get a fairly substantial amount of space for free. The occasional revive-in-place is nice, but again you can get some death metals for free and hang onto them for special circumstances where giving up progress isn't something you want to do, such as a boss at 10% hp.
Internet connection can be garbage to be honest. My ISP's service went down the toilet last weekend, like severe problems, and the game was still playable other than massive load times when the internet dropped below dialup speed. You shouldn't experience any lag, the game is played client-side, but menus, shops, and changing floors require you to ping the server. Had my connection drop off a cliff while changing floors once, and I just had to dismiss error messages for half an hour and eventually connection came back and I switched floors with no loss of progress.
