When I first started goldfarming, I did everything off the same IP. All my bots ran off my home IP and I also played on my main accounts too. The odds of your main account getting banned just because you were botting 1 account on the same IP is very very slim. As long as you don't bot your main account you should be fine.
Then again, there's no need to take unnecessary risks. If you buy a VPN or download a free one, both your bot account and main account will still be on the same IP, it just won't be your home IP. If you want to bot one account and play on your main legit and have them both on separate IP's you'll need to purchase a SOCKS proxy. This allows you to boot up the OSbot client under the IP of the proxy, so your bot will be using that IP and you'll be playing on your main account from your home IP.