1.7 gallon tank fish

that's a very small tank.

and if your guppies are a pair, you will soon have more fish than you have room for...

1.7 gallons doesn't sound like a very big tank, so I would keep the numbers low. It also depends what filtration/aeration you have going on.

Three or four more small fish, a catfish/bottom feeder and that's your lot, imo.

Having had many aquaria in my past, I would advise not adding any more than just one scavenger (catfish). and maybe another pair of smaller fish like a another type of tetra.

These fish you mentioned are all harmonious community fish. Of course, this assumes you're using proper thermostat-controlled heater (10-12 w) set to about 75-77 deg F, proper filtration (corner filter).

If you want more fish, I strongly advise adding a bubbling stone (aerator)...to put more oxygen in the water as fish thrive off it and allows a slightly larger group. However, I would switch to a minimum of a 10 gal tank.

A 1.7 gallon tank is generally used as a hospital tank to allow the nursing of a few sick fish back to health and isolate them from the larger community tank. Personally, I never used a tank smaller than 10 gallons as there's too much chance of problems and pollution and maintenance. In that 1.7G tank you should change over the water about 20-25% each week with fresh (de-chlorinated) water.