With your height it's 99% certain the Oasis is the tandem to go for. The alternative Outfitter is better suited to smaller/lighter people:
1. it has less buoyancy and IMO not really enough to support a couple of big adults - bear in mind that for a tandem it is a very short boat.
2. the floor of the rear cockpit of the Outfitter is too high for big feet - I found my heels tended to come awkwardly into contact with the deck at the end of every pedal stroke which was tiring and not conducive to long sessions
3. It may be a misperception because I don't think I ever sat in it but I think that the front cockpit was quite a bit shorter than the rear (might actually be only a few inches if anything but it certainly appeared to be that way)
Definitely you can solo them - on the newer model from the front or rear cockpit (steering in both) whereas the older model you had to solo from the rear cockpit. Soloing from the rear, the technique is to add ballast in the front cockpit; it may not be necessary to add so much ballast in the rear if soloing the new models from the front because your body weight will lie more centrally in the boat; others with this model may be able to advise.
Re the leg space: You should trial the boat for yourself but if that really is not possible then the following may help:- I am guessing that the distance between the seat and the drive slot will be pretty much the same between all the models. When I lifted the drive from my Adventure to use it in my Outfitter Tandem it ewas not necessary to readjust the pedals (confirming this assumption between Adventure and Outfitter rear cockpit only). The pedals are adjustable to meet the feet - further in for shorter pedallers further out for longer pedallers - and the drive functions exactly the same way irrespective of pedal adjustment. I am 6'2" & I am pretty sure that there's more than an extra two inches adjustment on the drive in my Adventure - I certainly don't have the pedals set on the fullest extension and if I remember right I think there are two 'notches' more length still to go when the drive is adjusted perfectly for me. It is going to depend on your particular shape and length but, on the basis of the above, my suspicion is that you should a) fit into at least one of the cockpits, b) be able to adjust the drive to suit your leg length, and c) get reasonably comfortable depending, of course, on your definition of comfort. Others may want to add their experience of the actual boat and/or a sea-trial will confirm this one way or the other.
Re your plan b: try the Mirage Drive boats first