Something like this will likely get the job done:
for (follower in haaretz_followers){
Sys.sleep(5)
haaretz_followers_info<-lookupUsers(haaretz_followers)
haaretz_followers_full<-twListToDF(haaretz_followers_info)
#Export data to csv
write.table(haaretz_followers_full, file = "haaretz_twitter_followers.csv", sep=",")
}
Here you're sleeping for 5 seconds between each call. I don't know what you're rate limit is -- you may need more or less to comply with Twitter's policies.
You're correct that the way you structure loops in R will affect performance, but in this case, you're intentionally inserting a pause which will be orders of magnitude longer than any wasted CPU time from a poorly-designed loop, so you don't really need to worry about that.