Frankenstien uberbass lefty neck question and more!

[the lowmax]

Though I do have a question, I'm really just thinking out loud. But I wouldn't mind some input on my custom bass. I'm building it to expand my playing, enhance my technique, and hopefully, get me laid. So far, I've only decided on the materials, for tone, function and feel. Vintage tint hi gloss (with 600 grit sanded satiny back) birdseye maple neck w/ Ebony board (for sophisticated and bright punch). Fretless (for tone and ear training). Antique white swamp ash body (for warm lumpy punch). Double Jazz Big Block pu @bridge(for bite), Precision pu @neck(for blurp) An ebony piano key cut in half lengthwise as a thumbrest between the pickups. Rear mounted knobs (2 volume, 1 or 2 tone), '62 style Fender tuners, a '74 bridge (all chrome). Bone nut (it's oldschool AND funny to say). As for
design... I'm obviously no purest. A P or J body (comfort/mass/style),
with a Lefty or Righty (string tension/looks), P or J neck (playability vs. finger training/mass), w/ Tele or Jazz headstock (funky or really funky). White pearloid pickguard or maybe none at all. Combining the best elements from all my other ax's. A true Frankenstien. Mwah ha ha!!. Phew. OK, it's out of my system. Thank you for listening. Anyway... My question is... If I get a lefty neck and string it upside down to use it righty, are the string tensions going to be noticably different. Another bassist told me the E would have less tension and would sound deeper. Isn't it the other way around? He swears by it and his 5 basses are either lefty strung righty or lefty necks on righty basses. How can the tension be different? I'm not worried about the neck twisting, as the neck will have a double truss rod and would be unlikely to twist or easy to adjust. Anybody have any thoughts?