1. Is Multibit as safe as Bitcoin-Core? if not why not....
It is slightly more susceptible to a coordinated attack. There are certain circumstances where an attacker with the right resources could isolate your wallet from the rest of the network, and feed it a false history. See Section 8. "Simplified Payment Verification" in the
original Bitcoin Whitepaper for more details.
Also, MultiBit re-uses bitcoin addresses for change, while Bitcoin Core uses a new address for every transaction. This increases the security of the cryptography slightly and increases privacy a bit.
In both cases, the security of MultiBit is sufficient for nearly all uses. These "weaknesses" are more theoretical, and require unusual circumstances before they become a problem.
I heard electrum has its own servers so if they are down your money is locked in there unless you have another wallet to access this wallet right???
There are many Electrum servers, and you could run your own server if you need to. As you've mentioned, you could also export your private keys from Electrum and import them into some other wallet if you find it impossible to connect to any Electrum servers.
2. I am guessing the private key for a certain address is exactly the same no matter where you retrieve it, whether, electrum, Multibit or bitcoin-CORE??
Correct.
I also have an Electrum Seed, what is this and why is this needed if I have a passphrase.
Electrum uses deterministic addresses. This means that every private key (and every address) that has bee generated by the Electrum wallet can be regenerated from a single secret piece of information. The Seed is that secret piece of information.
Bitcoin Core and MultiBit generate new private keys and addresses completely randomly. Therefore, if you don't have a good backup of every private key in the wallet, then it can become impossible to every determine what the private key was after a catastrophic loss. With Electrum, all you need to backup is the Seed, and with that one piece of information you can rebuild every address that the Electrum wallet ever created. Note, the Seed will not allow you to regenerate private keys that have been imported into Electrum from elsewhere, only those that Electrum generated.
The passphrase is used to encrypt the private keys after they are generated. This prevents someone else from getting the private keys form the wallet.
3. If I have 2 wallets open on my computer using the same wallet address , is there any upside or downside to this?
Yes. None of these wallets are designed to stay synchronized with other wallets that are using the same private key. They are all designed with the assumption that they are the only instance of a wallet with their particular private keys. As such, you can encounter situations where the balances get move to addresses that you didn't expect, or that one wallet is aware of a transaction that another wallet is not aware of. This can, at best, create confusion for you, and, at worst, lead to a permanent loss of bitcoins.
4. This is how I have protected my wallet address>>>>>>>>>> I have Both wallet apps encrypted with a passphrase I also have a paper wallet and A backup on my USB. Anything else?
Paper wallets are not useful as a backup for a Bitcoin Core wallet. Every time you send a transaction, Bitcoin Core creates a new address that it doesn't tell you about and moves some (or all) of your bitcoins to that new address. Make sure that you have
at least one good backup of Bitcoin Core stored in a safe place.
5. If I forgot my walletphrase from one walletAPP , BUT I rememeber the passphrase in my OTHER wallet app, Both these apps are the SAME exact btc wallet address, does this mean I can access my coins from the app that I remember the passphrase for and I can just delete the wallet app which I forgotten, possibly re-install the app then import the private key and make a new password which should then give me back access to that same wallet?? I dont get how this works. Eg; Multibit wallet address 1122 = forgot passphrase cannot access coins ------Bitcoin core wallet address 1122 = Remember passphrase means I can access the coins that were stuck in the multibit wallet. Does this mean I can NEVER use multibit ever again for this wallet? or by re-installing I can create a new pass?
Having the same bitcoin address on two different wallets that are both in use will lead to confusion and other problems. This is a bad idea. It is entirely possible that some of the bitcoins are stored associated with an address that you are unaware of. If you are lucky, you might be able to access your entire balance on one of the two wallets. In this case, yes, you could import all of the necessary private keys to the re-installed wallet with the new passphrase. If you are unlucky, you will lose bitcoins using this process.
I would like to have my bitcoin wallet on my phone, Is there a way to link my wallet to my phone for example if I am out somewhere and I decide to spend some bitcoin but I forgot to transfer some funds to my phone wallet, how do I access my main wallet? I think its just easier to use your main wallet everywhere Just like having 1 bank account ##, You access this account from an ATM, Computer, Phone app, Telephone Etc etc.... All links to the same bank account... I want to try do this with my BTC address, For now I will use my Computers and my Phone
Accessing bitcoins from your phone reduces the security of your wallet. If you are comfortable with your phone having access to your entire bitcoin balance, then why have the computer wallet at all? Generally, I put large amounts of cash in a bank, keep a smaller amount at home where I can quickly and easily access it, and then carry an even smaller amount in my "wallet" in my back pocket.
Giving your phone access to your entire bitcoin balance is a bit like carrying around your entire life savings in your pocket. This just doesn't seem like a good idea.
As has already been mentioned, the only wallet that I know about that allows you to access a single balance from both a computer and a phone is blockchain.info. This is a hybrid web-based wallet. You'll have to research it and decide for yourself if the security they provide is adequate for your needs.
