If I buy tickets for the back of the pavilion, are there chairs? Is it standing only? Never been there. Any advice appreciated!

Pavilion is all seats. People usually have folding chairs for the lawn area which is directly behind the pavilion.

Anywhere under the pavilion there are seats from left to right & front to back row. Then there is a walkway/corridor behind the back row separating the pavilion from the lawn seating (SRO) where you may use a blanket to park your rear or stand depending on whatever the show is you're seeing. Hope this helps.

Pavillion is all seated...lawn is standing room only.