Re: What size wire wheels should I get...13 or 14"?
In '85 base-model Crown Vics sported 14" wheels as standard equipment. This could very likely NOT be the case for an '88. I replaced my 14" rims & tires with 15" rims & tires. Reason for me was simple - there was a much broader range of tires available in the 15" size, and only a handful of (poorer-quality) tires available in 14".
If you like the look of the aluminum "spoke" rims that were put on many Crown Vics, Grand Marquis, and Lincolns in the early 90s, these rims are of the correct size & offset, and are a direct bolt-on to any 1980s Crown Victoria. You can pick up a set for pretty cheap from a wrecking yard, or e-bay. Only the centre caps were different - having the "Ford" logo, the Mercury Logo, or the Lincoln logo. I've got these rims with the Lincoln caps on my Crown Vic, and it doesn't look too bad at all.