NBitcoin is just a library that you can use to build some application around it. so depending on what you build it can be the same as Electrum or like anything else with any features that you like.
but Electrum is already a complete project (a wallet) with all the features already made by the developers and they have added the password thing so when you choose it you are asked for it.
as for being linked to a wallet, again if you are using NBitcoin, you need to write some code for your storage to store they keys that are generated. you can use a simple random generation of keys and store each of them each time a new one is generated or do what Electrum already does and use a Hierarchical Deterministic way of creating keys in which case you just store the master key or seed and each time you generate a new key it gets it from that master key.
be careful what you do though. security is a very important matter and not easy when you are trying to make your own thing!
there is also a chat room for it here:
https://gitter.im/MetacoSA/NBitcoin
