The following applies to audio interface.. as I've no experience with the BCF unit yet.
Basically, you install the interface driver and set the driver mode in Sonar correctly. Each interface may require different setup (turn off, install driver, turn on..etc..) Best read the manual first. For audio interface you will most likely use the ASIO mode (rather than WDM, MME, etc..) but it depends on your system. Some system gets better performance by using other modes, but generally ASIO will be the better choice.
Sonar works best with Win 7 or 8 and a current PC spec.. (Tascam website mentioned the US 1800 is tested on Win 8 too), go fully with 64 bits if possible. Common problem is the pops and clicks during playback, which can be diagnosed by running a system latency test :
http://www.thesycon.de/deu/latency_check.shtml And most of the time, it's due to wifi - turning it off solves most of the problem, or turn it off at least during Sonar session.
Play around with the audio interface buffer size - most defaults will work, but may not give you the best real time response. Not a problem if you don't have to monitor the audio real time, especially with vst effects. For example, if you're recording a band and everyone has their amp and you're just miking or lining in the audio - leaving the buffer higher should be fine and not having Sonar to echo the output.
If you're doing one track at a time, such as listening to Sonar playback while recording the track, echoing it's output with sound effects, then the buffer size needs to be setup just right, so you will get the lowest possible latency before pops and clicks set in. For this, you're probably targeting around 12 msec or lower round trip latency.
The other consideration is making sure your hard disk spin at 7200 rpm and not lower (green drive).
Those would be most of what I can think off at the moment .. at least some of my own experience when I got first got started.