Eric,
I just use a handheld glow starter to start my engine like normal and it runs fine inverted. I don't have onboard glow.
I don't have any experience with a 14 x 4W on a Saito 91. I just know that the 15 x 4W is working great on my Saito 100 so I would think the 14 x 4W would be good on the Saito 91.
Remember you should only be going to full throttle in vertical manuevers with this plane and even if it is a little under propped, you will be managing the rpm's with the throttle.
On 3D or fun-fly type planes, I like to have a prop that will rev up quickly and respond almost instantly to throttle changes.

Regads, Jim