Want to start but don't know how?

Hello everyone, I'm a 26 year old male who wants to start biohacking properly. In the last 6 months I did a blood test and have only been taking Vitamin D due to a deficiency. While training I take Creatine every single day and have noticed some of my ADHD symptoms decrease a little bit. But I want to go further. I am very skinny and try to eat as much as I need each day, weighing my food and tracking it, but it still doesn’t feel like enough, and a lot of the time I’m mentally fatigued. I’m also going to university and want to be mentally sharp and ready every day.

My main goals are to improve focus, energy, memory, and overall cognitive performance, while also gaining healthy weight and muscle. I’d love advice on where to start whether that’s supplements, lifestyle changes, sleep optimization, diet, blood markers to check, or any habits/tools that made a noticeable difference for you. I want to build a strong foundation and do this the right way, based on evidence and real results. Any recommendations?

Didn't know what flair to put it as, sorry.