You've run across a problem that haunts every new cyclist...buying too little bike to 'get your feet wet'. Everyone does it. If they don't, they get called poseurs or (incorrectly) Freds by the green eyed crowd

Without going an looking up the numbers, I'd day converting this bike to a drop barred road bike is something of a fool's errand (as are most conversions). If you go with STI (8, 9 or 10 speed), you'll need to change the shifters. Nothing else needs be changed (no matter what people tell you) but even that will be somewhat expensive depending on what level of components you buy. Shifters (STI) will cost around $200 to start (Sora) but expect to pay more. You'll need handlebars ($40 - $75), brakes ($35 to $60 a wheel), cables ($40) and tape ($20). That's pushing $440 at a minimum. Plus, assuming that you can't do the work yourself (being a newbie), you'll have labor added to the cost at around $45 per hour. I'd estimate about 2 hours...maybe 3. You are will on your way to a substantial percentage of a new bike by that time.

Better to just keep the Sirrus for commuting and buy something else for fun. Resale on bikes, even fairly new ones is pretty low. You'd be lucky if you could much more than $400 for the bike.

Think of this as one of life's expensive lessons. Buy as much bike as you can afford...you'll outgrow it slower.