What's the real risk of injury/hernia?

There is VERY little information out there about this, and believe me I have looked!

At this point your core is very weak -- you don't need to do things like sit ups to engage it and strengthen it, and any kind of "lever" motion like that is bad this early. The only ab specific exercise that I would consider safe after 5 weeks would be a gentle plank (start on your hands, like a push up position, instead of your elbows -- it's easier).

I think you'll be surprised to learn that easy jogging, especially when you transition from the elliptical to the treadmill, is a pretty good core workout. For that reason I would start with a week or two on the elliptical before you move to treadmill/outdoors. Personally I started running outside ~8 weeks post op and that was right for me.

I did not do any weight training while I had an ileo. The longest time between surgeries for me was 15 weeks and I did not feel comfortable doing weight training with an ileo that new. I'm sure many people will say that after six or eight weeks you're fine, do what you want. For me it was far more important to avoid a hernia than to do light weight training. I did go back to normal daily routine type stuff (so I probably lifted 20 lb worth of laundry, for example), but I stayed out of the weight room until ~3 months post takedown.

I agree that there are other options to strengthening the abs that are safer options for you, rather than situps and crunches.

Planks are great, as are stability exercises - have you heard of the Bosu ball? It's like a half circle that you can stand on (one or two feet) and it's a bit wobbly so it engages your core. You can also put your hands/forearms on it for planks.

Don't forget to also keep your "butt" tight - this will help with your takedown if you do go for the jpouch. Kegels helped me a lot with my jpouch, and also with this perm ileo (I was having some urinary incontinence with my recovery). There is lots of info online on how to do them properly, you don't want to feel your inner thighs tighten, you want the sensation to be that you are pulling the pelvic muscles inwards and upwards.

Here is a link to a good site:
http://www.urologyhealth.org/urology/index.cfm?article=119

It talks about Kegels for urinary issues, but the same info applies to your butt too :)

Six weeks after getting my ileo, they told me that planks were fine. Anything in which you push together or compact your midsection will put lots of pressure on it. Remember that any kind of weight training will also engage your core for stabilization. The other thing I would avoid are heavy squats - that also engages you to pull in your core and puts alot of downward pressure on your entire torso.

Look into a hernia belt. I'm on slow internet right now or I would look them up. It's a wide strip of elastic with a hole for your stoma.

I'm supposed to use an abdominal binder. Once again it's a wide strip of elastic as tall as your stomach. It holds you in.

I've found both through my supplier and the binder is also at CVS/Walgreens. More sizes are available from your supplier though.