Is it obligatory to make up prayers and fasts after years of masturbation without performing ghusl, given that the number or timing of these instances is not remembered? Is it permissible to forgo making up these obligations due to being busy or traveling? Is it sufficient to increase voluntary acts of worship instead of making up for them if making them up is difficult?

If you prayed without purity due to ignorance, then there is a difference of opinion regarding the obligation of making up (the prayers). If you choose to make them up, then make up what does not harm your body or your livelihood. Making up (obligatory prayers) takes precedence over voluntary prayers. The Malikis are of the view that making up two days for each day is sufficient. As for your fasting, it is valid even if you masturbated out of ignorance, so you are not required to make up those days. Do not pay attention to sudden doubts about an act of worship after completing it.