Ease of conversion to singlespeed/fixie is going to depend on the type of dropouts (rear wheel attachment). Since it's an older steel frame you have a reasonable chance of having the kind you need (horizontal, semi horizontal, or sliding), more so than a modern bike anyway.

A picture of First Love would be helpful.

Disclaimer: I've never actually converted a bike, but I've done a bit of research on the subject as I want a singlespeed/fixie myself.

If you do have the right dropouts it's a matter of picking a gear ratio that will work in your area and for you. I'd just talk to the LBS and then order from them if they have someone knowledgeable about singlespeeds and or fixies, the cogs themselves aren't expensive, so IMO it's worth paying for the expertise rather than having to buy multiple cogs to get it right. Sometimes you can use your existing crankarms/spider with the front chainring you need to make things less expensive, your LBS should be able to sort that out for you as well if it's possible (though singlespeed cranks can be had rather inexpensively as well). And, finally, a new rear hub/wheel which will probably be the most expensive piece unless you want to learn to build a wheel (then you can get a hub pretty cheap and rebuild using your old rim). Then you just take all the, now unnecessary, stuff off.

I think that would be a fun project. For other ideas, my first road bike is now my commuter.