The great thing about the chapel is that the stained glass windows provide a wow factor for guests so you don't need to go crazy with decor in the chapel (unless you want to). If you're on a tight budget, don't feel like you need spend hundreds of dollars on florals for the altar. Many couples have purchased inexpensive mums and they look great! The wonderful thing about Westminster is we have wood or white columns that you can use for any arrangement you purchase or rent (shown below). We also move any decor in the chapel to the reception room. Here are some examples of different decor that has been in the chapel:
If you're going to do any decor in the chapel, I recommend having something on the altar. My personal favorite are arrangements that frame the couple, just because they usually get the most pictures and it compliments the stained glass windows. Arches, pipe and drape, free standing frames are all allowed, but most couples don't use them just because it can take away from the stained glass back drop.
If there's room in the budget, you can absolutely fancy up the aisle! We've seen lanterns, silk flower pedals, LED candles, moss, pumpkins, signs, small arrangements and the list goes on and on. We do allow aisle runners, but since nothing can be taped/tacked to the floor I don't recommend it as I worry for any lady in heels who is already afraid she might trip.
You are more than welcome to bring in anything that can be hung from the chairs that line the aisle. We've seen signs, small lanterns, pomander balls, pew markers, tulle, small arrangements, etc. Definitely not a necessity, but depending on your colors/theme/style it can tie everything in nicely before guests see the reception.
House rules: We do not allow anything taped, tacked, glued, etc. to any floors, walls or ceilings. We also do not allow any real flower petals on the floor of the chapel--silk only. If you want to line the aisle with any candles, they must be LED. Real candles are allowed on the altar table only.