Having wifi and mobile internet on will run down your battery faster than if you don't have it on, but turning it off rather defeats the point of having a smartphone! I only turn mine off if the battery is nearly dead and I'm trying to scrape another hour or two out of it until I'm in a position to charge it. Just get into a habit of charging it overnight, if it won't last a full working day even with everything running there's probably something wrong with it.
I assume that you are on a contract or bundle that comes with a certain amount of data included. You should not have to end applications to avoid a huge bill, background use of applications (so with stuff running but the phone in your bag and not actively being used) is very small. If you are worried about going over your data allowance (after which you get charged extra), install a monitoring app. I use one called 3G Watchdog, it's very easy to use and will show you how much you've used and how much is left of your monthly allowance. It's also worth noting that the data allowance is only used when you're using the 'mobile internet', also known as 3G, while out and about. When you are connected to Wifi, either your home wifi or at a coffee shop/library/hotspot, it does not count - you can use the internet via wifi all day long if you like and you won't get charged or use your allowance. The phone will switch automatically, so if you leave the range of your home wifi it'll switch to 3G and back when you get home again. There should be a little icon, probably in the top of the phone's screen, to indicate which it's on.
You don't need bluetooth on to access the internet. In fact, I'd recommend turning it off except when you need it, because bluetooth sucks battery like there's no tomorrow and most of the time you won't be using it.
I don't know how much ram use is normal for your phone, and it varies hugely by model, so I can't answer that specifically, but I doubt it's a problem. The Galaxy Ace is an Android phone and Android is very good at managing its own ram and releasing it when needed; you more often find that if there is a problem, the cause of it is a badly coded app you've installed.
Hope that helps, if any of it doesn't make sense please come back and I'll try to be clearer!