At .01 SOL, it would take 10 million years, not 100 million. Slight slip of a decimal place, huh?

Question ... if the stars are 1-4 light years apart, can we fit 100 to 400 billion star-sized objects 1-4 LY apart in a disc that is 100,000 light years wide and 1,000 light years thick?

My brain is too tired to do the math right now.

Tic-toc ... whirr ... click ... grind ...

Solution hint:

1) calclate the volume of such a disc;

2) calculate the volume of something which has a diameter of 1-4 light years (this would be the space around each star ... forget about the negligible volume of each star itself) ... for convenience, use an average of 2 light years apart, which would require a spherical space 2 light years in diameter each, or 4.18 cubic light years around each star (4/3 πR³);

3) divide the first volume by the second volume, and that will tell you approximately how many will fit.

Oh, shit, let's just go ahead and finish the job. For the sake of simplicity, let's assume our galactic disc is the shape of a tuna can, although in reality it is more like a discus, thicker in the middel than at the edge. OK

V=πR²H = π * (50,000)² * 1,000 = 7.854 trillion cubic light years in the galaxy, which is enough to hold 1.88 trillion objects of 4.18 cubic light year size each. Yup, it appears reasonable that the galaxy is large enough to hold 100-400 billion stars.

Now, what stops them all from clumping together into one giant star or black hole due to gravitational pull? Seems like the space around each star near the galactic center would necessarily have to be greater than at the edge to prevent collapse, but it sure doesn't look that way because the star density appears greater at the galactic center.

Either way, we are doomed in only a coupl'a billion years cuz our big boy is gon'na go on the blink.