I assume you are using an alto-sham or hotbox for holding the hot items which should be ok to keep things hot. I would agree and say oven would be the best way to heat the things up. As apposed to a fryer. However, be aware of the different cooking times for each item and holding times. I would do the quiche and Rangoon last. Also do no not wrap those 2 items when you hold them hot as you will lose their "crispness" holding all that moisture will make them soft and gross. Proteins and starches are usually better at holding up in a hotbox. With exceptions, of course.

Oven

The heating time/temp sounds about right, depending on what size things are. But holding them more than 10 or 15 minutes after re-heating is going to give you one of two things: soggy pastry or breading, limp vegetables, etc, or everything dried up. If I couldn't serve them within 5 minutes of re-heating, I wouldn't do this kind of food at all. I'd pick something better suited to the facilities available. You didn't say what kind of food warmers they have at this place so I can't make any guesses about what's best to do.

I won't discuss the food safety aspect, how long at what temp for food safety. I'll leave that to someone with current professional knowledge of appropriate holding temperatures. I spent years working part time for a very good caterer and we served this kind of food all the time that we made from scratch. It was made but not baked, then frozen or refrigerated and taken to the venue still unbaked, and baked or re-heated on site and served as soon as it came out of the oven. We never held appetizers.

I am making some appetizers for my daughter's wedding in June. They include mini quiche, stuffed mushrooms, crab rangoons, spinach-artichoke-cheese bites, and petite stuffed potatoes. I have made some samples of these, then we will heat them up and see which ones handled freezing and re-heating the best. My question is this: what is the most efficient way to heat up frozen appetizers? I assume I can put them on a cookie sheet, still frozen, and bake at 350 for about 10 minutes? Does this sound right? Does anyone have experience with this? Thanks!!!

PS. There are large food warmers at our venue, so I need to figure out how early in the day we should start heating up appetizers. How long can they stay in the warming ovens? The wedding is at 7pm.

Thanks!!!