Great to hear you’ve got the bug.
I started out on a £350 Hardrock to see if I’d enjoy the riding and then jumped to a FS after test riding a couple of bikes (Reign and Trance). It seemed right at the time but knowing now what I do that wouldn’t be the path I’d take again with modern bike designs. FWIW I am now riding a steel hardtail with 150/120 adjustable suspension and quality components and loving it much more than the FS. it suits me, my ability, aspirations and trails I like to ride (inc local Surrey Hills, Peaks, Wales, trail centres)
You don’t need 3 bikes so the Hardrock should go, this will hopefully demonstrate to the wife that you are being financially responsible and that the bikes have a second hand value.
Whether you go FS or HT depends on where you ride and what you aspire to. Modern HT’s are very capable bikes and for the same budget you’ll get a better HT than FS in terms of components etc. Then you have the whole 26 vs 29 debate.
So try a few bikes, I’d suggest mid travel HTs (120-ish) and similar FS bikes (say 120-140) and then their 29er equivalents. There are lots of threads on here about bike choices. Then just buy what you like best.
@bwaarp’s post makes a lot of sense as does @wookster’s mention of coaching with Jedi – frankly a day with him will be the best money you ever spend on biking.