Are newer Porsches the same lug pattern as the old porsche 5 lug? What I am getting at is, will new porsche wheels fit on a flared 914 with a 5 lug conversion? Would the offset be a problem? Would the 17 or 16 inch wheels rub?

Same bolt pattern.
The 'newer' wheels have a higher offset, meaning they stick in further. Spacers are needed to clear the strut/rear inner wheel well.

Should fit flares fine with spacers.

You'll probably want to keep the diameter under the stock 25.5"

Shamefull plug here but I have some late model wheels for sale with tires at a really good price. I can send you pics and info if yout interested I live in the Bay Area (Redwood City).

So what would be the widest wheel I could fit with the spacers in the front? Same question for the rear as well. Also what size of spacer would I need?

with GT flares??

each car is different, you might be able to "borrow" a set from someone local or in the Bay Area for testing purposes

read these 2 threads, they'll give you the answers or at least they will give you the knowledge to find or figure out the answers:

wheel question 1

wheel question 2

widest I've seen on a regular GT flared car is 255/17 on the front and 275/17 on the rear.

do a search for "Porsche Thunder" and you'll find a pic of 914 with Boxster 16" wheels front/rear with no flares. It looks nice.

Here's an old pic on my 6r.
Front wheels are 18x8,no spacers,just the 914/6 hubs.
Rears are 18x10,2" spacers,and req'd 11"wide flares to cover'em.
Now that repo flares are available at a reasonable price I'll sooner or later ditch the fibro-flares and redo the body so it's all steel.
Ron