Investing in Stocks: Is it possible to manage both short & long term investment? Would it be more expensive & time consuming?

No. You should never manage short, only long. You set a threshold to wait for a stock to drop below for purchases, and you set a top at which you review if it makes sense to sell, to hold and set the mark higher.

Stocks are not meant to be a short term investment. If you try, it will eat all your time, and have little to gain from them. Study trends, and try to buy on the low end and sell on the high end. In order to know that, you have to study the company, what they've been doing right, what they are planning to bring to market, the likelihood that it will raise or drop prices and - wait/watch for the down turn, and buy. Or watch the prices rise and then eventually, when it hits your mark, sell.

No, it would not be more expensive. It would be more time consuming, but it is well worth it.