Electrical system question, what more can I add to the system? Options

[Fyrmdk914]

I have a 75 1.8. I just got this car about a month ago, and added a 300 Watt amplifir and a single 8" sub-woofer to the already upgraded stereo. Then, about 2 weeks later, my alternator died. I believe that this untimely death was caused by the additional draw on a 31 yr old alternator. I have replaced the alternator with a rebuilt stock Bosch unit and a new regulator. The system seems to be charging fine now. My question is this, How much more draw wil the system handle? I would like to upgrade to the halogen Headlight system, and add seat heater elements into the seats when I have them redone, (soon I hope, but delayed now due to the alternator expense!). I don't think that the headlight upgrade will increase draw much? But I am concerned with the draw from the heaters. I also realize that whenever I use the seat heaters here in So Cal, I will probably also be using the headlights, and I would hate to be in an either/or situation. Also, this car has carbs, so I think that I am saving some current there.