Hi experts,

I try to use Stata to conduct single imputation for three variables. Two are continuous and one is binary. I chose single imputation because previous literature suggests so.
I intend to use mi impute to conduct single imputation, because I cannot find any online resource on using Stata to do single imputation. All are about multiple imputation.
I read that we need to impute multiple variables simultaneously, so I chose mi impute chained, because this is the only version of mi impute that seems to me to allow for imputing continuous and binary variables simultaneously. So my question is I want to know if the syntax I wrote as below is correct or not.

mi set wide
mi register imputed var1 var2 var3 // var1 and var2 are continuous; var3 is binary
set seed 181123
#delimit ;
mi impute chained (pmm,knn(5)) var1 var2 (logit) var3 = depvar indepvars, add(1);
#delimit cr

Two potential issues:
Am I correct in using add(1) in mi impute if my intention is to use mi impute to do single imputation? Or should I first produce, say 20 datasets (add(20)), and then take the average of them on var1, var2, and var3?
Am I correct in relying on mi impute chained in performing single imputation for continuous and categorical variables simultaneously?

I know my question is awkward. Many thanks in advance for any advice!