A quick look at that tool tells me that

24 inputs, 1 output

will be approximately 5x the transaction size in kb

compared to

4 inputs, 1 output


And I'm still so, so lost on the whole 'prepaid transactions' thing. Will try to RTFM but boy, have I punished myself for not just going with a standard wallet.

Since we're on the subject of Electrum... once I manage to unload this 2fa-protected wallet...will STANDARD Electrum wallet do what I need it to do:

Collect small payments (0.5 mbtc to 5 mbtc each) for a few months from various senders, and then send the lump sum to another address in a single transaction

?

I used to use Bitcoin Core for this, and it worked like a charm. I am seriously looking at spending extra money for a large Disk just to be able to download 1tb of blocks and use that software again for this purpose.