Before Remy tells you this, I'll jump in first: Use the 58's for live reinforcement. They woldn't be my first choice for studio work, but theyr'e great live. They have a built in windscreen to start with, but I'd have a second one ready to go for each mic as well. (wind will ALWAYS show up at outdoor live events. Best to plan on it ahead of time...)

Try to use one mic for every two or four singers or so, depending on the size of the group and the number of mics you have, be it in pairs or in rows. Try to not have them in front of any one singer's mouth (unless they're soloists, of course). Since it's a choir, you won't want too much close-mic'ing per se, but you won't be able to get away with much distance type of mic'ing, either, not with a Live PA (unless you've got a LOT of gain before feedback, a great FOH guy, and other variables go your way.

When mixing, you can work out some kind of general stereo image (assuming the PA is truly stereo anyway). SM58's have a bump for low end warmth (the much-loved proximity effect) that may not even come into play when distance mic'ing, but even so, make sure you're not creating a lot of mud with the low end these mic's can generate, esp if you've got a dozen or so all pointing at the same source.

The 58's - being dynamic mics - are very forgiving, and when aimed & set up properly, can give you a great overall blend of a choir, esp in live situations. IMHO, the condensers are overkill for most live gigs, again, unless you've got a LOT of gain before feedback from the PA.

How big is the venue? Do you have lots of monitors and do you have at least two channels of delay?

Basically you'll want to not try any stereo micing techniques unless you have a good shell and some experience with outdoor reinforcement (vice amplification). I agree about using the 58s as the most expedient thing.

When I used to reinforce my Marine Bands the crowds were pretty large. I would place a couple of monitors by the stage for MC support. Then at stepped intervals I would place a row of wedges on the ground.

Each row was on its own delay (the send from an Aux). Sometimes I'd have three or four rows if the venue was large enough.

These lines of monitors were NOT pumping any significant volume at all. The goal is to magically hear the stage without being aware of the monitors. When I was done dialing in the delay, you could walk from the stage all the way to the back and never notice the monitors or notice any phasing of the stage vs monitors.

The beautiful part of this was that the entire audience could hear the performance without straining and the FOH "sound" was fairly invisible.

Sometimes I would use a stereo center array but many times I would be running just L-C-R omnis (or 58's) + mc/soloist wireless. Often if I could get out of playing, I would also do some spot micing and panning of the image. Of course, any version of my bands put out way more sound than your choir is going to produce but the principals will be the same.

My pics aren't as nice as Dave's but here is a very rough outline of a typical concert at Balboa Park or out by San Diego Bay. Coronado band shell was a sound nightmare not least of which because of the shell and dirty power so I varied that quite a bit from the image. Crowds typical numbered in the 1000 + size. For smaller crowds just start removing the outermost row(s) of monitors.

Thankyou! I will see what happens and let you know!