What RF transmitter and receiver to buy for long range
The range in RF communication is primarily determined by the Signal-to-Noise (SNR) ratio of the received signal and the sensitivity of the receiver chipset. SNR is directly proportional to the received power \$P_r\$.


  
  Does power determine range?
  


Yes, more power makes the range longer. But it is not a good idea to increase range by merely increasing the power as there are FCC regulations over max power that can be transmitted as well as more power may increase the interference in the nearby devices. Also, in order to increase the range two times you need to increase the power more than 4 times because of inverse square law. You need to study Friss transmission equation in more detail.

\$P_r=\frac{P_tG_tG_r\lambda^2}{4\pi R^2}\$

From Friss equation, you can see that there are other factors which we can tweak to increase the range (eg. antenna Gain and frequency). 


  
  Does 2.4 ghz go through objects?
  


Frequencies such as 2.4 GHz or 5 GHz get highly absorbed by bodies with high water content. So trees will tend to attenuate the signal significantly (if they are present in the line-of-sight(LOS)).There are drones which use these frequencies for remote control or video FPV transmission, but they employ directional antenna(antenna with higher gain) at the stationary side. You can do the same or use lower sub-GHz frequencies (such as 868 MHz/915 MHz ISM band or 433 MHz ISM band depending on your country). These lower frequencies have lower path loss and thus tend to penetrate longer distances with the same amount of transmitted power and antenna gains.


  
  What gives me channels? 
  


Channels are generally regions in the frequency domain which Tx-Rx uses for communication. Your Tx-Rx pair seems to use only one frequency of 433 MHz and thus has only one channel. But you can put any digital data (corresponding to the rotation, forward-backward movement) over this channel depending on how you design your data protocol. You don't need separate channels for transmitting different types of data. [Note: There will be limitation over the max data-rate that can be achieved over this 433 MHz frequency and that rate won't be sufficient enough for your video transmission.]

Also in multichannel devices, you can use only one channel at one time. The advantage of multichannel devices is that if some channel is congested then you can switch to other channels. 

There are many ready-made FPV Tx-Rx devices based on different frequencies. If you want to build it on your own then you need to first decide which frequency band you want to operate in and then look for the corresponding chipsets/modules which can give you desired data-rate. Only after you do the RF link budget analysis you go for actual implementation.

I hope it clarifies your doubts.