You are heavily borrowed at 600k against a salary of 100k in my view, but you have youth on your side in the event of any trip-up that sets you back a bit.
I would be more inclined to sell the overseas property (unless it is performing well and paying its way) and then leverage the 150K plus a small bit of extra equity from your home to get into a small commercial property with a strong return either in the UK or elsewhere.
At the end of the day, property investment is a good way to build assets and a future for yorself, but not at the expense of sleepless nights and poor quality of life!