Umph. Kinda right, sorta. Maybe not.
The 3300x, is very flexible for now, does great with many titles, almost as good as the 3600. So I'd agree with that.
You can always get a hdd later. $50 or less gets you a 1Tb that's decent and will have the room. The difference with the OS on a ssd is that everything is cached by the ssd. When you load a game for the first time, it first has to go through ssd cache. Where it stays. So once loaded, it'll run at ssd speeds, not hdd speeds. Steam, origin, all those get installed on ssd, their storage files on hdd. You access steam, it's all ssd.
SSD access read and write speeds are @ 5x faster than hdd.
Build looks solid for the budget, although I'm not a fan of the TT Smart series, they are wimpy and low quality, made more for an OEM grandma's websurfer replacement than a gaming pc. They don't take hard hitting gpu usage well. A decent quality 550w would be better, not because it's 550w, but because it's not a mid-low end psu that is usually in the 500w level. There really aren't any decent 500w I can think of off hand. But a lot of gaming quality 550w/650w.