In trading or any other method, don't need to sit 24 hours just to do this so take this bitcoin job only as a part time.
You are right, you need to have a big capital for starting it since 1 mining rig isn't enough for it, so you will need to buy a lot of mining rigs maybe 4-10 mining rig will suffice your daily income for being a full time bitcoin miner.
even if you have enough capital to build yourself a decent mining rig, you first need to earn back your money which already is a very though job as the difficulty keeps increasing. by the time you have earned back around 50-75% of your money, it will not be profitable to continue mining with the same rig.