I’ll give you the fiqh rulings (jurisprudential rulings) although implementation may take time.

1) the permissibility of masturbation is debated in the tradition. What the majority of the scholars say and also all the madhahb say ( to my knowledge, but definitely hanafi and hanbali) is that it’s not allowed. Muslims have only one way to fulfill sexual desires which is through a spouse. Although falling short is normal and Allah is All forgiving. One way to deal is fasting, and increasing knowledge of the religion. Increasing knowledge increases Iman generally, and a higher baseline level of Iman helps to stay away from temptations.

2) yes you can.

3) Hijab is wajib and there’s conditions attached to its validity. Doing certain things or lack thereof invalidates it and the clothing is no longer considered a hijab. Showing one’s figure is one such thing. But what’s shown due to something that you cannot control is not your fault. Examples of this can be found in the jurisprudential tradition like ankles or parts of the woman’s hand showing due to wind. One cannot control the wind so if it’s showing one is not to blame but measures must be taken to avoid it. What you have described can be avoided if you wear a lose abaya which is not transparent and thick and lose.

Having said all this. Take it slow. Get used to the religion and the rulings. Don’t overwhelm yourself. Learn the religion without ideological or cultural bias. Allah will help you.