Now I normally build 1/35 Armor. Big lumbering brutes covered with dirt and stowage. However, last week I won a 1/48 scale Spad 13 and thought I would give it a try. Being marginally familiar with this type of aircraft, I need some help.

Paint - glossy? flat? Did they use a spray gun or were the planes brush painted?
Guide Wires - the kit comes with steel wire. Would it be easier to string the guides with monofiliment?
Weathering - what type of wear and tear ocurred? There's not a whole lot of metal on these planes. Does the paint streak after contact with the fuel and oil?

Thanks for your help. Oh, and buy the way I'll try to keep the grime to a minimum and no external stowage.

That's a great plane !
What will be it's colour ? green or tan ?
On all the areas covered by fabric or wood (everything except the engine cover), you'll need flat paint. My guess is that the planes were hand painted, with a brush.
If the fabric is tan, then it means that it was not painted, left in it's original color.

There are two 1/48 Spad XIII kits I know of, Aroura/Glencoe and Dragon/DML. In either case, these links may help:

Glencoe 1/48 Spad X
DML 1/48 Spad XIII
Dragon 1/48 Spad 13

In relation to your specific questions:
Paint was generally brushed, and had a slight sheen to it. Rigging is a personal preference, I'd be leaning to how the last article above details it - kit supplied stainless steel wire for the landing gear and rudder control rigging with invisible thread painted black used for the strut rigging.

As for weathering - can't help there sorry. I'd suggest a fair bit of oil, but I cannot be sure.

Cheers,
Linz