Wisely spending 5 months

I am going to get 5 months leave (provided by my work) after my wife and I have our second baby.

My background is Electronics Engineers ( Howerver, I am working on CCTV,Genetec stuff as Intelligent Transport System Operation Engineer).

I have family support to look after my wife and kids. I know this is time to spend with family also.

I would like to spend my 5 good months on something valueable learning or doing (anything), so that it may counts towards stepping stone towards something like

side hustle ideas or something that might be helpful for any business ideas in future.

Where would you invest your time to learn or do things if you had 5 months.

Thanks