1: What's the easiest way to make money? People keep mugging me and taking what little I have.
Easiest way right now, is going to be item flipping (buy items for the city, selling to item market), you can also looking into selling bounty slots. Once you hit 15, you'll unlock flying and see an increase there. Alternatively, you can, and should, join a good faction that pays for assists in wars. To stop yourself getting mugged, use ghost trades until you unlock the stock market
2: wise uses of energy?
Train your stats, up to be able to beat the majority of people on bladr's list, then attack until you're 15, use the leave option for best xp gains
3: which crimes should be focused on first?
Search for cash, do crimes in order.
4: which medicines should I hang onto and which do I absolutely not need?
Join a faction, meds will be provided free, if they're not. It's probably not a good faction.
5: What supplies should I absolutely hang onto versus which ones to sell?
Most temp weapons are worth holding onto but see above, a lot of your supplies will be faction provided. This should include your weapons and armour. And you should hold onto and use any Xanax you find.