Q: How to operate a lower power thermistor power circuit? I would like to like to create a temperature circuit that connects to a wireless module (e.g. Bluetooth) to transmit the signal. My challenge is that I have a limited power supply (200 mA - 3.5V) to power both. Therefore, I would like to use as little power as possible for my sensing circuit.
Sensing circuit:
For my circuit, I would like to use a thermistor. Since thermistor resistance change with the change of temperature leading the sensing of the thermistor to draw more current. I was thinking of adding a large resistor in series to keep the current draw low since the voltage will be regulated.
Is that a good approach? what problem might it cause? Is there a better alternative?

A: Using a load resistor is not only a good idea, it's simple way to measure the thermistor with an ADC. The thermistor and load resistor form a voltage divider, so you measure the reference feed voltage, then the divider, to derive the thermistor's resistance.
A way to save power is to only power up the reference feed voltage to the divider when you're taking the measurement. Then there's no standby draw.
Also you can use higher-value thermistors, such as 10K ohm. Then the required current is smaller.

A: 10k and 100k are common thermistor values.  If you do the voltage divider method, the current will be pretty low.  Usually you need an opamp to read/buffer it, and that will pull way more current then the thermistors.  If you can go directly to an A2D you can save that current, but again, the current to run the A2D can be much more than the thermistors.

Another method is to use a current source instead of a voltage divider.  You can put 100uA through the thermistor and read the voltage across it with an A2D. Again, the A2D will pull more current than the thermistor circuit. You may have to check the voltage overhead to use this method depending on the temperature ranges and specific thermistor you pick.

A: You don't say what temperature range you expect to cover, but in practical cases the thermistor is not going to see more than 1mA at a volt or two because otherwise self-heating will destroy your accuracy. So it's going to be pretty negligible in comparison to 200mA.
In a battery-powered situation there are various tricks that can be used to reduce average current to microamperes such as using relatively high value thermistor and buffering it (or using a low voltage oscillation circuit as is used in inexpensive consumer thermometers), only powering the measuring circuit long enough to make a measurement and then turning it off, and so on. Completely unnecessary if your circuit is mains-powered.
Thermistors do have quite a bit of nonlinearity so if you expect to cover a wide temperature range accurately (or even without ugly visible steps in a digital display) you may need a lot more resolution in your ADC than you would initially guess. A 10K (at 25°C) thermistor may change about 100:1 over the range of -40°C to +130°C (eg. from ~300K to ~3K). On the other hand, they're ideal for comfort temperature measurement, just use a series resistor  near the thermistor value at the center of the range, so for a 10K at 25°C thermistor you would use a 10K 1% resistor.
