Hello, new member here. I picked up an M6R earlier in the year and immediately fell in love with the versatility of this bike (and I'm not new to folders). It has re-kindled interest in short touring for me, and I've had some of the same questions/concerns as you.
I added Ergon GP2 grips (2 finger bar end) and they do not impact the fold, and I think GP3s and even GP4s would be fine - as long as the bar ends are set toward horizontal (not ideal, but perfectly usable), there's a lot of clearance around the wheel when folded to accommodate longer bar ends. You can test this with a coat hanger wire model bent around your current grip.
Assume you set the seat far back on the rails for more reach.
I just did a reasonably easy mod of cutting/installing a plastic tube to cover the bottom of the "U" in the M bars which gives me an additional lower aero position on the M bars. This one really helps against headwinds, and when I get cruising at higher speeds - still testing (this one takes a while to get used to) but I'm finding I can cruise in a higher gear more often and it's comfortable for me as I'm used to lower bars on my other bikes.
I'll second the MKS quick release pedals if you go SPD, but I'm running half-clips on the stock pedals from Alphabet Cottage and quite like them... and they don't affect the fold, or speed of folding (like the MKS).
For touring, I'm into ultra-light backpacking and using the same gear can tour out of the single front T-bag <20lbs, including ~5lbs of food/water. Can't express how nice this set-up is for traveling - I'm nearly the equivalent of a standard 2-item carry-on air traveler, and I've gone through plenty of stores, restaurants, grocery stores, and museums with my full touring rig in shopping cart/stroller mode. I advise the X-roller if you plan to "stroller" as much as I do. There's a couple of other neat tricks/options for carrying everything if you're interested.
Hope that helps.