You need to learn funnels if you are going to have an online business. Russell Brunson teaches funnels probably better than anyone and his software ClickFunnels is among the best on the market.
An autoresponder service is a must so you can build your audience and reach out to them via email. An email list is an asset you own and can send value or offers to any time.
AWeber has been around for a long time and are very dependable. They also happen to have a free option (up to 500 subscribers), which is great when you're starting out.
To build your Twitter account, you need to post consistently. HypeFury is the gold standard in terms of Twitter automation services. It will post your pre-written Tweets at scheduled times, post to Facebook & LinkedIn, and create images of your tweets for use on Instagram. It really does have it all. Get a 14 day free trial here.