(a) Nope, he hasn't met the mother yet.
(b) We did get confirmation that within 36 months his first child will be born, which makes her 15 in the flash-forwards. So he has 36 months to meet the girl and knock her up, or marry her I guess.
(c) The starting point back in Season 1 is relevant, because Barney marries Robin and Ted meets the mother at that wedding. So I guess it's fair to start with how he met Barney and Robin.
Of course, the whole thing IS ridiculous - how my parents met takes 10 minutes to tell - but if you were concerned about the story taking too long to tell, you'd think the show had gone on too long after like 6 episodes.
I agree that Jason Segel is better than the show, and there has been a lot of material lately where he seems disengaged and bored. He's basically being marginalized, because he and Hanigan are having a baby on the show, which means all the jokes they're gonna get from now on are "parenting is so hard" jokes. Ugh. Annoying.
However, I will say that Season 7 had some darn good episodes in it, if you know where to look. "Ducky Tie," "Trilogy Time," and "Now We're Even" are quite funny, and aside from a stupid subplot in the latter, the two-episode arc "Rebound Girl"/"Symphony of Illumination" is one of the 4 or 5 best things they've ever done. Of course, what they all have in common is almost minimal obsession with who the mother is.