Intonation. So many things can effect intonation
Fretwear! Yes, any fretwear will ruin your intonation even after a set-up. If your having intonation problems with your open chords then it's probably worn frets. A high nut will cause this as well as too light of a string guage with a heavy hand. You should be able to tune the open strings with a tuner and just play. If you are tweaking your tuning then something is wrong. I can help figure this out for you. And of course saddle adjustments after neck and action is set. I use a analog strobe tuner to set intonation
Earvana nut is a quick fix to open chord tuning problems. I've been able to get guitars/players to play in tune without it.

Buzz Feiten: If after a proper set-up and fretwork you still hear an intonation problem then the Feiten system may be for you. It involves installing a new compensated nut and tempering the intonation to Feiten's specifications. It's the same idea that piano tuners use to temper the upper register of a piano.

"I want low action with no buzz"
Hmmm, well the two don't go hand in hand. Generally the lower you go the lower the "threshold of buzz" is. But I can work with you and find a good compromise. Good fretwork will help, (lower action will show any fret imperfections), as well as heavier gauge strings. The heavier the gauge the higher the tension hence a higher "threshold of buzz". "Threshold of buzz" (t.o.b.),is the point that you hear fretbuzz. At some point round wound strings will start to buzz. Depending on your style of play, fingerboard and body woods, all effect the t.o.b. Maple and ebony fingerboards tend to be brighter than rosewood and may enhance buzz. Cast saddles and bridges tend to have less tone and enhance buzz while steel saddles and bridges enhance tone and decrease buzz. Blues and Bluegrass players want a high threshold, so in turn we use heavier strings and higher action. While speed metal players that use high gain prefer very low action. The high gain settings will alleviate the low t.o.b. Most players prefer something in between these set-ups.
Flatwound, half-wound, coated, silk and steel, all have mellower tone and may be an option for you.

First Set-up: I'll ask a few questions and you can try some of the shop guitars. With this information I will do my best to get it right for you the first time. If you want any adjustments after playing it in the shop or at home for a few days I will make them at no charge.

Student set-ups. The most important thing for a new player, especially a child, is ease of play. Most new acoustic guitars come with come with "light" acoustic strings which are actually too heavy for a new player, and the action is always too high for them. I'll flatten the neck with an adjustment, lower the action, and resting it with Silk and Steel strings. These strings are an extra light gauge with a silk wrap over a steel core and are easy to play without hurting the fingers. It's nice to play an open g chord with no pain! As the student gets better and stronger we can go up one gauge at a time for bigger tone.