A '78 Summicron is a great choice.
A Summaron is a very good lens,indeed.
As for Jupiters: please see the article at Apugger Dante Stella's site: http://www.dantestella.com/technical/compat.html
The whole Jupiter / LTM problem seems to boil down to ( simply ) there were different specs for Soviet LTM cameras than for Leicas
My own experience with Jupiters (very good) is on SLRs and Contax/Kiev rfdrs, where the LTM problems don't exist.
I'd go for one of the CV lenses, and get shooting.
They are excellent lenses, and a great value.
When things settle, and you're really flush, snag one of those 35/1.4 ASPH s... in the meantime make some great pictures with the CV..