at the time of starting the network does not need? Starting MN can also through the signature transfer from offline mashine?

there I won't be able to use my key that I remember by heart. Electrum can it?

I want to sell the apartment and buy a masternode, how to run it from a cold wallet, so my key could not see the network?

Nope, someone edited original title of the DASH's OP, and when you quoted their posts to discuss, you automatically spred out incorrect title. The first one started there, https://bitcointalk.org/index.php?topic=421615.msg51168867#msg51168867: then logictense is another user spread it around. It's a big surprising to know that even you did not notice the title when you quote and post, so it's normal to see new joiners of the thread unintentionally help to spread the wrong topic title around.  

I recommend Tungi17 to spend a few minutes to correct subject title of your old posts (I listed below) to official topic title: [ANN][DASH] Dash (dash.org) | First Self-Funding Self-Governing Crypto Currency So, your post's subject should be: Re: [ANN][DASH] Dash (dash.org) | First Self-Funding Self-Governing Crypto Currency
Your posts should be corrected are:
https://bitcointalk.org/index.php?topic=421615.msg51217718#msg51217718
https://bitcointalk.org/index.php?topic=421615.msg51204380#msg51204380
https://bitcointalk.org/index.php?topic=421615.msg51204420#msg51204420