270 mio is by far enough for an exploration conda - if you settle for a 7b fuelscoop instead of a 7a, and maybe take b-class afmu instead of a-class, you'll end with ~190 mio.
i just would suggest that a) you fly the conda first before deciding to spend a year in it, as quite some commanders hate it for its supercruise handling and landing characteristics (i personally like it above the AspE, but i'm taking a DBE for this trip) and b) that you anyway do a short exploration tour with at least 150 jumps, that's around 3000 ly and back in an unengineered conda. the circumnavigation will take over 9 month...
generally you'll find always helpfull very seasoned explorers in the expeditions discord, so you'll learn a ton. i wouldn't care about credits, because upon return we'll all have data worth 600 mio/cr and more. but whether you are already up for such a trip, only you can tell. it took me personally triple elite and over two years to get ready for this!
