Funeral service presentation – mixed size photos and colour and black and white – what size do I need to set the photos at and other queries

I am using Movie Maker for the first time, with photos and music.  It's for my brother's funeral.  The photos are a mix of b&w and colour and I am planning to put a couple of Beatles songs in plus Cat Stevens.  

I've scanned a series of old black and white photos which vary in size from about 3 inches to much larger ones.   At the moment I only have access to a Flip Pal scanner which scans at 600 dpi.  I also have more recent digital camera images which I will use and they will be uploaded directly from my PC or from SD cards.  

I was planning a section on his early life with his parents and my other brothers.  Mostly, those are in b&w and smaller than the later digital camera images.  I was then planning a section on his life with his partner and their children and also a section on the things he enjoyed - fishing, cricket on the beach (I'm Australian), his dog, playing cards etc.

So my queries:

1.  Sizing for the photos to be uploaded.  Do I need to adjust photo sizes for Movie Maker?  I have GIMP as a photo editor.

2.  I was planning to do this on PowerPoint but the funeral home does not use that and has said it needs to be Movie Maker.  I can drop heading slides eg. Mike's Early Life at the start of the first section into Powerpoint.  How do I do this with Movie Maker?

Thanks all for your advice.

Anne