How do others safely spend large amounts of bitcoins? I know of Armory, but I could prefer to use Core
I'm not certain, but my impression has always been that those that want to manage large amounts of bitcoins offline typically use Armory. That's what I would use if I was going to try to access a significant amount of bitcoins from a paper wallet.
I thought I could simply use the Bitcoin core GUI, and then dump the signed tx ... and broadcast if from another PC. However, the offline machine would need a copy of the blockchain.. and the "bootstrap.dat" option is no longer available.
Hmm. I suppose you could install Core on an online computer and allow it to get fully synchronized. Then you could copy the bitcoin folder onto a removable hard drive and install that on the offline computer. You'd then be able to create the transaction (or transactions) with the GUI. You could extract those transactions from the offline computer and use sendrawtransaction on the online computer to broadcast them.
Keep in mind that if you don't use coin-control the Core wallet will generate RANDOM addresses and send the change from the transactions to those
RANDOM addresses. As such, you will no longer have any bitcoins in your original paper wallets. You'll want to make sure you either use coin-control or send
ALL the bitcoins to new paper wallets.