Printing/Hosting/Sizing Beginner Question

[LillyElla]

Hello. I am looking for some advice. I have started taking some photos for family and friends and I want to be able to make them available in a professional manner. I'm not charging for the photos so I don't want to lose money by paying for a site to host them. I have a couple of questions regarding printing and hosting.

Where do you recommend I have my photos printed at? I sent a few samples to Walgreens, mpix, and prolab express just to compare the quality.
When I got the photos back from prolab express I noticed a flyer they included about a free site that does hosting and fulfillment (they take a percentage of your profit from each order placed).

Do you have a preferred lab and/or hosting/fulfillment site?

My other question is about resizing an image for printing. I am new to editing so I only know the very basics of photoshop. I have made a template for 4x6, 5x7, and 8x10 in photoshop and I drag my image into the template and adjust it accordingly. Am I going about this the wrong way? If I size an image in photoshop to be a 4x6 and someone wants to order it as an 8x10 how would I do this? Aside from asking the person what size they think they might want on every single photo. I thought about sizing all of them bigger and then it can be cropped for a smaller print. I feel like I a missing a piece of the puzzle and making things much harder than they have to be.

I would appreciate any advice. Thanks in advance!
S