Thanks for all the advice. I don't need access to the BTC - my motivation was to move it to a new wallet as Multibit Classic is no longer supported. Now that I've managed to import the private key into Electrum, I'm happy.
I intend to keep this BTC for as long as possible as I think Bitcoin will carry on increasing and if it goes up a couple more orders of magnitude it could make a big difference to my life.
Also, the guide I'd read about how to claim my BCH said I ought to move BTC to a different wallet first just to make sure - any advice there?
Who knows where on chain fees are going to end up in the future? I'd definitely keep my eyes open for slack periods and consolidate all of those inputs into one if the cost falls enough. The heat is on fee wise at present because of BCH and probable spamming, but it'll slacken off soon. Just a few weeks ago you probably could've sent that through for 1/10th of the cost or less.
I had a balance with something like 30 inputs. I waited until things were quiet and sent them all to one address. I think the fee was about $25 but I didn't want it marooned there in some super expensive future.