Electrical – convert a single circuit with multiple lights/1 switch to control 1 light/switch

Conversion is too soft a word for what will have to be done, it is more than likely going to be a rework.

Somethings you need to figure out:

I would like to add a ceiling fan/light to one of the receptacles

A ceiling fan is far heavier than a recessed can light and thus needs additional support. The recessed light box will need to be replaced with a special box that braces itself into a ceiling joist or into a wooden block between two ceiling joists. Looking at how the recessed light box is being fastened into the ceiling will tell you how to do this.

and convert the other to a track light with its own light switch control.

This can be done but even in the best case scenario, you will need to run an additional cable from the switch gang box to one of the luminaires. This is of course assuming that the cable coming from the breaker is coming into the switch box.

It becomes more complicated if the power to the breaker is coming into one of the two lights. In this instance you would need to run a 3 wire and ground cable from the switch box to the light with the power line coming in:

NOTE: All of this of course is assuming that if one of these happens to be a fan/light combo, then the fan and light will be wired to turn on with a single switch, rather than separate switches for each function.

NOTE 2: This also assumes that you have already have a double gang box for installing two switches. If you do not have one then you will need to open up the wall and install one.

NOTE 3: The following diagrams assume equipment grounds are properly wired throughout.

This explanation assumes you are trying to control both sets of lights at the same time and not independently.

If they are on the same circuit, having separate hot wires to each switch is really redundant. The return wires from the switches are not.

There is no problem ganging both lighting fixtures on the same switch so long as the switch is rated for the power the fixtures draw. Most modern dimmers are rated 150, 300, 600 or 1000 watts. You need to make sure that the two fixtures, added together, are somewhat lower than the switch rating. If not, your gonna need a bigger switch!

All you need to do is hook one of the hot lines to the switch and cap the other hot line with a wirenut. Then pigtail both of the two switched lines (that return to the fixtures) to the switch output side. Do be sure to attach ground, for safety and to reduce the chance of random hum.

All of this assumes that the dimmers are suitable to the type of lighting (special dimmers are needed for many CFL and LED bulbs), that they are single pole (not three way), and there is no special feature requiring a neutral.

SUPPLEMENT

As Tester101 needs to regularly remind me, current code calls for a neutral wire at all switches. You have an extra wire in the switch box (the redundant hot) that could be converted to a neutral if you ever need it. You would need to switch it over at the fixture to the neutral white line, mark it at the fixture to show it is neutral (e.g., with white tape) and mark it at the switch box as neutral (also white tape).