We should never think that once we have given some money and time to the Lord that the rest is ours to do with as we please. All that we have belongs to God, so He should be taken into consideration in everything we do.
Few people make a living as a public speaker but many people build it into their career. A career is like a suit of clothes: to look its best, it must be tailored and accessorized. So whatever career you choose, let's say it's social work - you can, for example, ask your boss - if you can give talks at housing project community centers about the social services available.