[Solved]-Formatting Highcharts plot via rCharts-Highcharts

Hi @user2691669 welcome to SO. I will try to address your 4 questions.

1. To set style use a marker with option symbol = your style
2. To remove markers use a marker with option enabled = FALSE
3. To not have a series show in legend use showInLegend = FALSE
4. To interpolate missing values the best i can offer is connectNulls = TRUE

Your code can be written to implement the above as:

set.seed(123134)
y <- rnorm(20, 35, 4)
y[7] <- NA
y[13] <- NA
y <- rbind(t(t(y)), t(t(rep(NA, 10))))
fc <- rnorm(10, 35, 1)
fc <- rbind(t(t(rep(NA,20))), t(t(fc)))
uci <- rnorm(10, 38, 1)
uci <- rbind(t(t(rep(NA,20))), t(t(uci)))
lci <- rnorm(10, 32, 1)
lci <- rbind(t(t(rep(NA,20))), t(t(lci)))
plotData <- data.frame(y,fc,uci,lci)

h1 <- Highcharts$new()
h1$chart(type="line")
h1$series(data=plotData$y, marker = list(symbol = 'circle'), connectNulls = TRUE)
h1$series(data=plotData$fc, marker = list(symbol = 'circle'), connectNulls = TRUE)
h1$series(data=plotData$uci, showInLegend = FALSE, marker = list(symbol = 'square'), connectNulls = TRUE)
h1$series(data=plotData$lci, showInLegend = FALSE, marker = list(symbol = 'square'), connectNulls = TRUE)
h1$series(data=rep(30,30), marker= list(enabled = FALSE))
h1

The various options can be seen at the HighCharts api documentation. For example the marker options are found at this link.