There are some bits of advice that are less tangible than HUD/monitor advice, but probably more useful. The firs - and it may seem obvious - is add one table at a time. It's astonishing the difference simply playing 2 tables has on your game - it's like your thought processes are suddenly interrupted, and it takes a few thousand hands to get used to it. Beyond that, it does get easier, but I still recommend you add gradually as there is inevitably a period where you're playing sub-optimally - and tilting on 4 tables is a lot more dangerous than tilting on one.

As for the HUD argument, I find it very useful when determining my autopilot plays. Tricksier play, though, will always require specific reads as well as HUD info.

HUDs aren't completely necessary at microstakes since we're playing mostly ABC.

They're not completely necessary, no, but I argue we're not always playing ABC. Because there are more players who are wildly sub-optimal at low stakes - whether nitty, passive, loose or maniacal - we want to have this info to hand when we find ourselves in pots with these guys, and an HUD is a reliable method of reminding ourselves and playing accordingly.