You're well on your way to becoming your own decorator, but you've still got a few more things to learn. The next step is to budget your shopping list.
See my advice for budgeting when you read more.
To get started, look at your floor plan and figure out where the negative space lies and what you need to shop for. Now, do your research and figure out a price range for each item on your list. For example, you might be able to find a side table on Craigslist for $40 and give it a paint job, buy an affordably priced one new for $130, or buy a high-end one for $400. Prioritize each item on your list. I recommend investing in larger pieces like sofas, coffee tables, and secretaries, and cutting back on smaller furnishings. But, you might also want to invest in a piece of artwork, which you can use as a jumping off point for the design of your room. Figure out how much you can afford to spend, and how much you expect to spend on each item.