I would like to say as much as possible but it really depends. The more the better but life circumstances can limit how much formal education some can get.
The first question to ask is about your goals. Are you looking to get ordained by your denomination? Some denominations have specific educational requirements for ordination. My denomination seeks a Master of Divinity but not every denomination does.
If the main concern is gaining the knowledge or ministry experience, Bible college can be a good option. I have taught at the undergraduate level at Emmanuel Bible College and Tyndale University College and I have been very impressed at the quality of the students.
While you don’t need to attend seminary to be a pastor, I do recommend it if possible. I have studied at McMaster Divinity College and Acadia Divinity College. Both are excellent seminaries. Even if you can plug away at seminary over a number of years it can be beneficial. Most seminaries allow you to audit a course at lower cost and with requiring you write assignments.
What about online and non-accredited schools? It depends on your goals. If you are seeking ordination, make sure your denomination will accept the school. Take a course and see if it is meeting your learning needs. Beware of diploma mills that cater to people’s desire to have a degree without requiring any academic rigour.
And remember that theological education is not limited to a college of university. Determine to be a lifelong learner, whatever that may look like for you.
You can be pastor without a Bible college or seminary degree. Technically, all you need is a congregation that will call you as their pastor. But don’t take short cuts when it comes to your theological education. Take a look at your goals and your resources (time and money) and put together a plan that works.