How Long?

How long can i use a nute water before i should mix a new batch. Do i have to mix a new batch every week or what? Also, how often should i feed? once a weekish?

you need to search feeding schedules, its endless friend

What type of medium are you using? If it soil then only water once the soil is dry. If it is a hydroponic grow then it all depends on what type of system you are running. If it is soil I would suggest only mixing up what you need to water at that time, then next time mixing more. Your plants demands for nutrients are going to change from week to week especially in flower. Keep it as simple as possible until you get the hang of things. What type of nutrients are you using?

change the water when the plants dont like it no more or you need to change nute mix.

Organic nutrient solutions can be refrigerated a couple of weeks before they go bad. They can be frozen, pretty much indefinitely. What ingredients you use and how they are prepared will affect shelf life. Orange juice lifespan might be analogous to the average organic fertilizer solution. Chemical fert useability varies greatly from lasting forever to the same lifespan as organics, depending on what kind you use.

You should alternate feedings with plain water. A good schedule would be water, let soil dry until the top quarter or so is completely dry, fertilize, let soil dry, water again, etc.