For your first question, you can use the glue package to embed expressions within curly brackets, which then gets converted into a string
library(dplyr)
library(glue)
mydf <- data.frame(means = round(runif(n = 10, min = 10, max = 15), 2),
sd = round(runif(n = 10, min = 2, max = 5), 2))
means sd
1 10.90 2.79
2 12.06 4.83
3 14.87 3.51
4 12.35 2.67
5 11.08 3.13
6 10.76 3.44
7 14.04 4.05
8 10.78 3.96
9 13.31 2.86
10 13.35 2.82
# create a new column called `together` with the means and SD in parentheses
mydf %>% mutate(together = glue("{means} ({sd})"))
means sd together
1 10.90 2.79 10.9 (2.79)
2 12.06 4.83 12.06 (4.83)
3 14.87 3.51 14.87 (3.51)
4 12.35 2.67 12.35 (2.67)
5 11.08 3.13 11.08 (3.13)
6 10.76 3.44 10.76 (3.44)
7 14.04 4.05 14.04 (4.05)
8 10.78 3.96 10.78 (3.96)
9 13.31 2.86 13.31 (2.86)
10 13.35 2.82 13.35 (2.82)