First welcome to the forum and to pontoon boating.
I'm not going to help you much I'm afraid, but I think your motors are all about the same as far as reliability is concerned, there is nothing at all wrong with the Etec 60, I would love to have one hanging on my boat.
I have always been a fan of Crest Pontoons, but I haven't looked at new ones in a few years so I can't say much about any of the ones you mentioned.
The 70 Yammy power plant may have a tiny edge with the 4 stroke and extra 10 HP. There are many forum members running 4 strokes and doing there own maintenance, I don't think there is a lot more to it than there is to taking care of a garden tractor or 4 wheeler.
Which ever rig you choose, choose it and don't look back. Be happy with what you get, forget about the others and get busy enjoying the pontoon lifestyle.
Once again, welcome to our forum.
2006 Forester 19 Fish (new deck and carpet, Pontoonstuff interior, 2019)
1996 Mercury 50 ELPT4S
1983 Sea Nymph FM171 Striper (complete rebuild from hull up, 2014)
1985 Johnson 70 J70ELCO
Raystown Country, PA