I read all of the OP's responses and some of the other posters, I have a few things to comment on. I tend to babble so I'll try and make key points instead so this might actually be read.
FLASH - don't discount that you will never use it. If you do any kind of portraiture or nudes, you certainly will invariably need flash if you are going to improve on and "create and mold" light rather than just read what's there...
BE PREPARED - my 5D Mk II got wet from hurricane sandy and I had to send it for repair. I needed my Sekonic 756DR(or whatever the numbers are) for my flash settings or I would have had to cancel shoots. If nothing else keep the Minolta, it has the most options overall and is probably the one you will get the most from, and in the movie industry I hear nothing but sorrow over how great minoltas were, though they now hail the Sekonic the same way, but still miss the Minolta, use the rest of the money on equipment you will use now and by the time you need a meter for flash (which I don't think that Minolta can do?) you will want to buy something newer than the other two anyway.
NIGHT - I have 2 Sekonic meters, one is from like the 50's the original Studio Delux and the newly acquired 7xxDR and neither can meter as far as my 5D Mk 2 by a long shot... I don't actually understand EV admittedly, but I know that my Sekonic won't go past 8 seconds and my 5D goes to 30...
THE FUTUTRE - similar to you my original Sekonic Studio Delux I got while buying a bunch of old gear and played with it for a day, then put it in a box for 2 years while I learned more and one day discovered that I needed it because I was noticing I was over exposing my digital images because the back of the 5D was telling me that the image looked good but at home on the computer I had blown out highlights. The meter on incident mode with a model tells you a lot more about how the light is hitting her skin than your eyes can descern from looking at the back of the camera.
POLAROID - I can feel the grumbling as people here tend to get ornery about the "D" word... Your method is just like PRO's did back I'm the day when they checked with a Polaroid... Which also wasn't EXACTLY the same as the film would show just as digital isn't the same as film in exposure, you just have to learn your system and know when to adjust and by how much. Same with film, every 400ASA film will not expose exactly the same, you will learn your film and adjust accordingly too.
SPOT - can be invaluable to a night time long exposure if there is even one bright thing out there that you want to have NOT overblown.
MORE FUTURE - you never know what you'll discover later, I really didn't think at 12 years old that I would ever need this viewfinder thing my dad had in his camera kit, nor this external flash thing that would flash when my on camera flash would go off. I just now at the age of 30 got a rangefinder that needed the viewfinder lines that were on the thing and I'm glad I kept it. I'm still looking for that flash thing, I JUST found a use for it and I'm kicking myself that I can't find it, it was a cheap, square plastic flash only, it didn't connect to anything (no flash sync cable or flash foot) and only took one AA battery, it reacted to other flashes going off to trigger it, it was tiny though and in my fine art project I'm currently working on, it would be the PERFECT thing, they don't make them anymore and were so utterly useless I'm sure almost all were thrown out years ago... Point is, keep at least one because you never know when you might need one. There's a reason almost any pro photographer has one.
ADVANCEMENT IN LEARNING - I too used to use the back of my digital for exposure, now as I've grown, the only thing I sweat about is if I forget my meter. Given all the gear you've amassed the past year (of which I'm very jealous of your 4x5's as I have everything but the body, perhaps when you move to 8x10 you'll remember me hehe) you may advance very quickly and find use for the meter very soon. But three is silly... Keep the Minolta, ditch the others for gear upgrades/film
Hope some of that was valuable and good luck!
The Important Ones - Mamiya: 7 II, RZ67 Pro II / Canon: 1V, AE-1 / Kodak: No 1 Pocket Autographic, No 1A Pocket Autographic
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