Down-scaling PC size planning help!

[Toxiic]

I've been wanting to make my PC smaller for quite some time as there is limited space inside my room and I know find it unnecessary to keep a large tower on my desk or on the floor. I have been debating whether to transfer my system to to a smaller case such as a GDO7 to make use of my current atx Asus Z170-A or whether I should bite the bullet and begin buying parts to build a mini-itx pc (motherboard, case and probably psu). The maximum budget for this is around £300 (GBP) and keeping the cost as low as possible would be greatly appreciated.  

 

Current PC: http://uk.pcpartpicker.com/list/QhXhkT

[Zoya Mist]

Honestly I would try try putting everything into the smaller case first before you buy a new mobo and other stuff because if it does end up fitting inside without any problems then you will save a good amount of money.