I am a chemist and RO water is practically as pure as you can be as a starting point. Any ions you want require salt additions. And pH adjustment will swing wildly without buffering.
I always calculate how much priming sugar I need for the batch I intend to bottle, make up a solution with water of a known volume (n bottles x 5 ml) and boil it to drive oxygen out and sanitize. I then use an eyedropper to add 5 ml solution directly to each bottle before filling.
Mashing is an enzymic conversion process of starches (polysaccharides) to simple sugars. Ions and pH both play an important role in that process (calcium in particular). You don't want to mash in zero TDS water because the pH will swing widely and the efficiency will be low. Concentrations of...
After the boil, I filter my wort through a 400 mesh bag into the fermenter and cool it in there. I always get a clean yeast harvest after fermentation is done.
Dissolve #bottles x 5 oz (~1 tsp) priming sugar in clean water and boil it to sanitize. Divide the total volume up by #bottles and dose each sanitized bottle with that amount of solution.
Then fill and cap and let sit for a week at room temp.
But I would use a campden tablet to convert any elemental chlorine or chloramines to chloride. It's commonly found in drinking water as a sanitation agent.
You didn't say if you were monitoring the gravity. Even if it was done, you could have leave it in the fermentation vessel for more than a month without a problem certainly more than 18 days. But a stable gravity is the only reliable indication that it's done.
After my boil I always strain my wort through a sanitized 400 mesh bag. Never have any trub to deal with. The bag is in a bucket with a spigot which I use to cool the wort. Then I drain it into the fermenter through the spigot.