3x a week is good as it's a balance between rest days but still enough for good consistency.
I'd recommend going to parkrun. It's free and has everyone from the super-speedy to gentle joggers and leisurely walkers. After growing up with PE teachers that had a somewhat rigid concept of what a being a runner is, it's really helpful to see an inclusive running community. Indeed my puce-coloured PE teacher ranting about harder and faster was infact totally and utterly wrong about how to begin to run!
Spend 5-10 mins buidling some bodyweight strength exercises into your cool down. It's easier to remember and less intrusive. I find the doorstep is great for prompting me before entering the interference of the house, and also a useful prop.
Not al runs will be the same. Some will click. Some will be hard for any variety of reasons- weather, hormones, when you last ate/ drank etc. One hard run is just one hard run- the next usually clicks back in better.
You won't need gallons of water. Drink well in the hours before a run so it's in your system, but being summer and working hard as you get started, it can be worth having a small bottle to keep you refreshed. I've got 150ml bottles that fit in pockets. I take one sip at a time, swill it in my mouth then swallow so it's more about freshening up than drinking a quantity.
Don't run on a full stomach, 2 hours tends to be recommended after full meals. A light snack can top you up if you're otherwise running on empty. It can take experience to get comfortable with running "fasted" on no fuel e.g. in the morning.
Following the plan to get to 5k is an important first stage. After that there's options about what to do with running. Life will probably get in the way at some point. My first C25k involved delays and disruptions of mastitis/ bronchiolitis, suddenly returning to work and just general life with a baby/ toddler, and it took 5 months from start to finish. I then had a goal to run further to take part in an event, smashed that, then found myself talked into my first half-marathon all within a year!