Shorty....since you had no probs before you fitted the alloys, it's obviously nothing to do with your car and has to be the alloys.
Have 'em balanced and if they're not bent or buckled, they should then be fine.
What you don't want, is to find that a wheel in bent (like I recently had with my 17's!) 'cos it means forking out for a new wheel! (like I had to!)
Loudandproud....yep, could be any of those but always do the cheepest first, i.e. balancing....it's the usual cause of wheel vibration in most cases.
I had it bad in my Cav recently.....I thought it was a dodgy ball joint or track-rod-end 'cos I've had them on and off so many times lately (playing around with different suspension set-ups), the rubbers on 'em are fooked.
I thought "it can't be the balancing, 'cos the wheels have only just been balanced!"
It turned out that they were out of balance and that the place that balanced them the first time had an out of calibration machine!
Once balanced "properly" at a different tyre shop (who discovered they were both out by 20) the vibration was gone! (almost)
I say almost 'cos I've still got some 'slight' vibration but I know that's down to the near-side outer CV being on it's way out.
Try doing a circle in the car with the steering on full lock....and try it both ways.
If it's a CV going, you'll hear a definate clonking noise, like I do when turning right on full-lock.