Clydesdales/Athenas (200+ lb / 91+ kg) - Fixing up Shogun from the old days/ Starting at 247 lbs./ Questions

Hello Every One,
I've been reading the sticky's and doing searches but still have a couple of questions/thoughts. I'm getting back into riding and after obsessively searching for a new bike I fell in love with a older Shogun 500 that reminds me of a bike I road in High School. I'm happy with the bike but I'm tweaking it some. Ok, two main questions today.
1. What tires do people like to ride over roads and greenways? I've ordered these- http://www.amazon.com/gp/product/B000A0KZ1O/ref=oh_o03_s01_i00_details
knobby hybrids-27/1 3/8in. (75psi)that I thought would absorb some road shock and be more stable on the slick parts of the green way. I'm taking off a rear Panaracer/Tourgard 27/1 1/4in. off the back and a 27/1 1/8in off the front and after reading some threads about weight and tires I'm thinking I may be heading the wrong direction? Loved riding low profile knobby s in collage on touring frame but that was 20 years and 65lbs. ago.

2. What is the difference between 27' tires and 700c tires- everybody talks about how they ride different but I cant figure out what the size difference is? or what the bike requirements are the change? I know it must be simple but i just have not found it.
Ok thats it for today-
really inspired by some of the post in this section. I'm hoping to get down to 185lbs. I'm 43 with my first little boy turning 17months. I've got a long way to go being a dad and I'm not getting any younger. Tired of making grunt noises when I get up and down. Want to ride with my boy when he's ready.

Sheldon Brown has it all on this page: http://www.sheldonbrown.com/tire-sizing.html

He explains that the 27 is bigger than the 700c, so the tires will not exchange on eachother. I've experienced it myself. My Bridgestone had 27's and I put newer 700c on it. Luckily my long reach brakes worked okay and just had to move the pads lower.

As for the tires, my first question always is "what size is your rim'? The same Sheldon Brown page has a chart at the bottom with recommended sizes for specific rims. On my roadbike I have a 15mm width rim and I use a 28mm training tire. I could go up to a 32, but it doesn't fit under the fender. On my touring bike I have a 17mm rim and use a 32mm touring tire. For my weight (220lbs) the 32 mm tire has been very very comfortable and I enjoy the ride a lot more than the 28mm, but it does go a bit slower. The Kenda you've chosen looks like a very comfy tire and I'd recommend it if you are going to be doing some gravel and packed dirt. If you're going to be doing a lot of paved road, you may find it slowing you down some though.

Thank You Rona,
I'll check out the link, but very cool answer! I can get my brain around it now. I'm out riding in Nashville on a greenway and downtown right now. Really nice to be out riding again.
- Ben

I'm about about your weight and ride both 700x 25 & 30 Panaracer tourguards, love'em. The 30's suck up bumps and are ok fine for Greenways. Experiment with your tires, you'll find what suites your riding style and terrian.