Soil Pipe and vent move to outside?

[5035]

Hi everyone I am a confident diy chap but I've never had to get near to a soil stack before (lucky me) My problem is that I am refitting my small en-suite which had a boxed in soil pipe and AAV. To give me room to fit a sink unit I would like to move the whole lot out through the wall then back in to the stack (which is boxed in in the room below) Outside I would fit a conventional vent instead of the AAV. The soil pipe from the WC to the stack is only 450mm long. As the new arrangement will have a couple of extra 90 degree bends to get along the outside wall then back in again, will this degrade the efficiency of the soil pipe, perhaps increasing the chance of a blockage? Also will there be enough of a fall along the pipe? Photo of existing set up attached so you can hopefully understand my garbled explanation. thanks in advance. Mick