Hi Amy, and welcome to the site. Being a guy who likes to fix stuff there's some information below to get you started, I hope it's not too much:
When using a respirator, be aware they come with different levels of protection. Most of the retail varieties are rated at N95, meaning they filter 95% of the common particulates. You can get N100 or P100 respirators on ebay or online allergy sites which filter 99.97% of common particulates. The latter should work well for manual sanding, and if you want even more protection just wrap a bandana around the outside of the respirator when wearing it. Plus, IT LOOKS COOL!
If you use a chemical solvent you'll want to go to the next level of protection which is the half or full mask respirator with interchangable filters on each side. Be sure to check that the particular model is rated for vapor protection. This will also come in handy if you decide to paint the bike yourself. Home Depot carries these but you'll pay more there than if using ebay or google shopping.
Using eye protection when sanding wouldn't hurt either, nothing to report there.
You may want to consider wearing latex gloves so the paint doesn't get under your fingernails. I use them when sanding or removing a greasy chain just because it makes cleaning up a heck of a lot easier. You can get latex gloves at any major retailer. And with lead paint, be sure to sweep and dust the area afterwards so all the lead is removed.
