Replying to comments on your own post is entirely appropriate and highly encouraged, just make sure it is unique and thoughtful rather than literally copy/pasting the same thing.
The Steemit FAQ offers this Steemit Etiquette Guide which will answer most of your questions.
In general, I would avoid any bots that are not clearly reputable and instead https://steembottracker.com/ is a trusted source for promotional bots. I'm not sure if anyone deals with that sort of abuse, but you could ask in steem.chat here and they would probably know better.