Should I say "Velisne/Velitisne panem?" To mean "Do you want/would you like some bread?
Or would I use Visne/Vultisne?
So, would I use subjunctive to ask or the indicative mood?
The subjunctive in Latin tends to indicate potential, possible, or unreal actions. To my ears, velisne? means something like "potentially, in the future, might you want it?"
The indicative, on the other hand, indicates actual reality. Visne? sounds more like "do you, at present, in this actual reality, want it?"
So I would use the indicative here. You're asking about the state of actual reality. Latin doesn't really use the subjunctive for politeness the way English does; the main place where the subjunctive is polite is for giving suggestions instead of commands, but even then, the imperative is used even in prayers to deities (so it's not particularly rude).