1 - Not sure about recommending a running club as I am not a member of one but there are lots in Belfast.
2 - Plenty of decent long run's close by, I am on the Donegal Road and either do my long runs past your's and up through Belvoir and down then Ormeau Road. There also a nice loop past Sir Thomas and Lady Dixon park and back along the A1. The Lagan tow path is also very popular for long runs and is nice and flat.
If you need hill work I would suggest heading from shaws bridge up through Belvoir its only about a mile away from you are or if you want real hurt like hell hills you can run up Divis/Black Mountain.
Also you are close to 3 parkruns, Queen's Parkrun, Falls Parkrun or Ormeau Parkrun. They are definitely worth checking out.
3 - I am starting training for the Belfast marathon soon and will be doing my long runs Sunday morning if you ever fancy a few miles.
As recovery runner said Mizuno do 2 shoes designed with forefoot strike in mind (they have the wave cushioning just at the forefoot). They are the Levitas and Cursoris with the Levitas being the more minimal shoe.
I have the Levitas and really like them, if you shop around they can be had online for £50, also if you like Saucony and want something more minimal then the Kinvara 3 can be found at the same price, they don't have specific forefoot cushioning but they are a great shoe for mid/forefoot strikers.
I am not the typical shape for a runner either, I have only recently stated doing parkruns so my pb is 21:01.
I was in a simillar position to yourself last year before my first half marathon, aimed for around 1:37 and actually finished in 1:34:04. I am not sure about the GNR course but would guess its fairly flat, if you are doing hilly 11 mile trail runs then 13.1 miles on the road will be grand.
As Seth says body shape isn't always an indicator, my GF's brother is 6''3 and well built but can easly put me to shame over any distance.