It may be useful for you to define a concatenation operator for characters. Sometimes, I find this is more intuitive and handy than using paste0 or paste. Also, it makes your code look better when you have nested paste, e.g.paste0("Y~",paste0("z",1:3, "*x",1:3,collapse="+"). The drawback is that it may reduce the readability of your code to other R user, since it is a self define function.(i guess it should be fine, cuz it is really intuitive. Also other scripting language also has similar concatenation operator)

"%+%" <- function(...){
paste0(...,sep="")
}
> "hello" %+% "world"
[1] "helloworld"
"hello" %+% "world" %+% 1:3
[1] "helloworld1" "helloworld2" "helloworld3"

Generating formula:

"Y~" %+% paste0("z",1:3, "*x",1:3,collapse="+")
[1] "Y~z1*x1+z2*x2+z3*x3"