I know this question has im sure been beaten into the ground farther than MJ (to soon? )

im installing  a 5" spoa, 1.5" OME springs (rear up front conversion so rear springs all the way around) and 1" shackles,  i have been told that anything smaller than a 33" tire would look kinda goofy

-First what tire size would you recommend? 
-ill be doing mainly trail rides(2/4wd) some rocks and some mud if i can find it.  im thinkin SS LTBs bc they are the cheapest but i know theyll wear faster than a radial, so any other ideas?  price is my biggest factor but id like something more aggressive than a street tire (like TSL/SSR/LTB/Baha Claw/Ground Hawg instead of an all terrain). 
-Next, if i went with 33s would i need to change gears?  right now i have the 1.3, still like to be able to take the back roads to work if possible, what gears would be best?

You'll definitly want to go with lower gears with any tires larger than 29".  Your stock engine will thank you for it.

Rocky Road has a good tire and gear calculator here:
http://www.rocky-road.com/calculator.html

You might want to go with the 2" Lift Trail-Tough Bonz-Eye Leaf Springs instead of the OME 1.5" ones for a SPOA.  Most people who have run the OME in a SPOA have said that it is a little to light of a leaf spring for that configuration.  What about a SPOA and a YJ spring conversion?

You could just do a straight SPOA and run 31" tires, but what fun would that be. 

Most people who have run the OME in a SPOA have said that it is a little to light of a leaf spring for that configuration.

what do you mean too light?

Probably axle wrap?

Axle wrap, as unbridled said,  and the spring will start to loose it's arch after a while, dropping the amount of lift you have.

and suppose they are already in my garage, any suggestions?

i just added a reverse shackle2 inch  lift kit  from Calmini, lift was closer to  2 3/4 of and inch, my new 235 75 15 tires just barley clear the front bumper, and I could defently feel the loss of power going from 215's to 235's

and suppose they are already in my garage, any suggestions?

Run em, see how they do.  Not all experiences are equal, they might work great for what you want to use them for.  Then next time someone asks you can pass on what you found out. 

assuming they work almost as well as they are supposed to, would 31s be a bit on the small size?
What would be the cheapest/easiest way to gear down?

It's kind of a wash cost wise between a T-case gear set or diff gears, but, for the money, you'll get a much lower crawl low with the t-case gears.

how difficult is it to change either?

I like to have a shop do either in case any shims are needed.  It can also be as easy as pulling your T-case, sending it out as a core and buying a T-case with the gears already installed, but it's more expensive.  You might just want to troll the vendor's sites and see what's available.  I know Rocky-Road, Calmini, Petreoworks and a couple others carry both.
If I was to do either, the T-case gears would be easiest.  It used to be where I'd even dig into trannies with no fear but I can't get around as easy anymore