Do I use a different sign for 'go' and 'goes'?
No, ASL does not change verbs based on the subject like English does. You will use this exact same sign for 'go', 'goes', and even 'went'. The context of your sentence will clarify who is doing the action and when.
Can I sign this with just one hand?
The standard dictionary sign uses both hands. However, in casual or fast-paced conversation, you might see fluent signers use a one-handed version. For beginners, it is highly recommended to practice and use the two-handed version for clarity.
Should I move my hands straight forward every time?
Not necessarily. If you are talking about someone going to a specific place that you've set up on your left or right, you can move your hands in that direction. Moving straight forward is the default, neutral way to sign it.