-Do you have your own marked lane or will I have to share a lane with someone?
Shared lanes is norm. Obviously ppl try to space out & don't share if a lane is completely free to choose instead.
-If the latter, how do I make sure I don't get in their way?
Since you are doing breast stroke then I'd say choose a lane with another breaststroker (then you only scratch & kick each other & hopefully not ppl in adjacent lanes)... just try not to kick too wide and make it easy for someone to get past if they are faster. My main pool now has lanes only 2 persons wide; most pools have large lanes that up to 4 ppl can swim abreast (if doing front crawl), so the faster ones can ovetake on the 'inside'. Overtaking is unusual in the slow lane unless someone has stopped completely, though.
-How are the lanes marked? Will it be obvious?
Sometimes marked by suggested speed, sometimes not. I'd suggest you go for slow if there is a choice. A lot of ppl in slow lane may soon annoy you, they may stop suddenly in random places(!)
-If my technique is terrible, will people notice?
Maybe, but who cares? No one is perfect, ppl just want to get on in their own way not get concerned with what others do.
-Do I need to wear a swimming hat and goggles or can I just tie my hair up?
That is individual pool policy, ask them. I can't swim without goggles & hat but I only do frt craw.
-Is there any other etiquette I need to be aware of?
Bit of give & take goes a long way, the 'etiquette' depends which lane partly, tbh. I am told by slow lane swimmers that other swimmers bobbling aimlessly is a rampant hazard for them. Patience will be your friend. Pausing at the wall to see if a faster swimmer is trying to get past you is considerate. Slow lane swimmers tend to hate anyone splashy but you won't be splashy anyway.
-What time of the day /day of the week is generally quietest?
midday, when working people can't get there, or any time 9am-4pm really. Evenings & early morning usually are busiest. Your individual pool may be able to advise, too.