What to do with 60+ glass bricks?!

Not necessarily a problem. ( If you drop one, then you will have an even number... )

7x7 would require 49.

5x5 would require 25.

3x3 would require 9.

Lots of other non-square combinations will result in odd numbers as well.

I suspect getting additional blocks would be quite easy as well.

Are there enough glass blocks to make a top cap for your garden wall, which can then be illuminated as part of your interactive projects?

You could perhaps turn them into scaled up pixel strips. Attach them to plastic lawn edging for the strip and space them out proportionally. 

Or you could perhaps turn them into modular light blocks by setting each of them into its own wooden frame, which can have connection options both mechanical and electrical.

Could do Solas type stuff but on a larger scale.

If you are into extreme plumbing, then you could plumb them together and pump coloured liquids through them. I've seen a couple of designs where with careful selection of liquids then you can alternate colours as they are pumped around the system, then have them separate back out again on the return flow. You can end up with an organic lava lamp sort of effect if done right. (or probably a complete mess if done wrong...)

MSGEQ7 based audio spectrum analyser

7 frequency bands so that works out well for rainbows as well...

7x8 matrix = 56 blocks

7x9 matrix = 63 blocks

Odd number might work out better as you can do a centre zero stereo mode with left channel up and right channel down.

You could use them for edge lighting outdoor paths or steps (which might be in-keeping with your rainbow staircase).

Similarly, you could use then to edge light garden decking or perhaps a stage, or a slightly raised garden border.

Could make a cube shaped planter out of them 4x4 on each side.

Or a round wishing well with an apex roof that has solar panels to charge batteries during the day for powering the lights in the evenings.

61 of them would stack into a hollow 6x6 pyramid (it worked for the Louvre in Paris).

If you have 60, then that would allow you to do some sort of an analogue clock with divisions for 60 minutes / 60 seconds.

Sticking with clocks then you might be able to build a giant 7-seg display timer out of them.

Sticking with circles, you could use it for angles (6-degree intervals), compass rose, etc.

Divide them into two semicircles and you could have stereo VU meters, perhaps augmented with a LED pixel strip / EL wire on a servo motor as the twitching needle.

Light them up individually, as Dave suggested and then have them play Conway's game of life.

If you put "one-way" mirror film on both back and front of each block and addressable LEDs on the sides, you could create a really wild reconfigurable building block infinity-mirror sculpture.

You could make a fairly unobtrusive 3D printed frame for each block that interlocks horizontally to adjacent blocks and hides wiring. Pillars at either end would vertically lock the rows of blocks.

Nice idea.

Other cellular automata are available too