900 MHz I/Q Direct Conversion SDR
The PA doesn't have a BPF directly on its output prior to the TR switch. It's likely it will need one and the one at the antenna should be repositioned to take care of that. Having a bi-rectional BPF for transmit and receive directions is overly complex. If you need a BPF at the input to the RX LNA then put one there as well.

Of significant concern is the software loop to keep the synthesizer perfectly lined-up with the incoming received signal. This isn't a crit but an observation about the synth - it has to be capable of almost analogue resolution. You give no clue about this so I'm making this point!

I also observe that the IQ demod chip is 5V yet the LTC5599 only works from 2.7 to 3.6 volts (I'm planning on using this part BTW) - this means a more complex power supply regime but, maybe you have that stuff covered.

That's me done!