There are some websites devoted to cake decorating, like "cakecentral.com" that could be of help. You may want to check out some YouTube videos. If you're near a city versus out in the country, adult ed or craft stores or cake decorating supplies stores might offer cake decorating classes. HTH!

Some tips:

Clear a bigger work area than you think you'll need, including an extra counter space not attached to where you're actually working to set things down on.

Have a jar of warm water and some lint free tea towels at hand for wiping off your implements and messes.

Keep your work area cold. Keep your frosting cool.

Make more frosting than you think you'll need.

Don't spare the sugar. It's the sugar that holds the shape. Sugar water is traditionally used to stiffen everything from doilies to hair curls.

All butter may be too soft. Shortening tastes nasty. Combos are trying to balance those ideas.

Use a flower nail and shears to make and place flowers. It's much easier than building them on a cake.

Turntables make things so much easier, especially for full sized cakes. If you don't have a decorating pedestal, you can use a lazy susan under your cake dish, or even just a piece of cardboard which is easier to grab and turn without disturbing the cake.

If you have a way to raise your cake or cupcake, like a pedestal, it'll be easier, unless you're short. If you don't want to store or serve the cake on your pedestal, you can put your dish or drum on the pedestal. A silicone potholder will help keep it in place. Cupcakes are easier but you still need to be careful of the frosting when you grab them. A piece of paper underneath, so you can slide to the edge of the pedestal or dish, can help.

Don't put frosted cupcakes in a cupcake holder where they sit close together, especially in holes, until you're done and they've had a chance to firm up some.

If you want to practice without making a bunch of cakes, You can frost styrofoam forms, food containers, bottles, and whatever detritus you fancy. In some cases you can just scrape the frosting off, back into your pastry bag and go again, though you might need to chill it first.

The real secret is practice. Once you've made a hundred roses you'll wonder why it was ever a second thought. Good luck!

Lots of good info there! Thank you!

I have been looking at Youtube videos, which is where I got the idea to just do large roses for now. I like the ones that are edged in color but I have to find a video for those.

Can anyone address my other questions about coloring and coupler/bag size?

Should I stick to Wilton products? It looks like Michael's is phasing them out in favor of a brand called Celebrate it. JoAnn's has a much larger selection of Wilton.

Wilton products are basic, work fine and cheap. I prefer metal tips for decorating, though I have a plastic Wilton press/tips which I love for things like devilled eggs. I think my other tips are Ateco, which is also pretty basic. Check online at professional cake decorating suppliers for the range of brands and what's available. Educate yourself on supplies while you're learning. I'm firmly of the opinion that the best tools are better for less able/experienced practitioners, because they're unlikely to know how to make do, whereas experts can make poor instruments sing. If I were you, I'd start with a few pieces while you're learning and when you've mastered the basics and are ready to invest in a variety of tips and tool, choose the best available in your budget, even if you have to order it online (or by mail) rather than buying at a craft store. Do check if there's a local restaurant, or especially bakery, supply shop near you.

Here's a link to the Wilton page on how to use a coupler. The size of the coupler doesn't matter. If it's too big for your bag, cut a bigger hole. The recommendations are about how much frosting you'll need for bigger decorations which is what bigger tips generally are used for, so bigger bags give you more room for more frosting. You can even cut a corner out of a ziploc, drop a tip in and pipe. And if you're good, you can cut holes in the corner of the bag and pipe without a tip.

Just make sure your tip fits your coupler nicely. It should drop right in but fill the hole firmly.

To get a colored edge, you just make a line of color in your bag. Rather than wasting paragraphs, here's a video which shows how to do it with both gel color and with colored frosting. She's not doing precision work, just demonstrating the concept, but it's very clear, I think, in how it's done. For precision, make neater lines. :) Really. If you're using a flat petal tip, line up your color lines to the edges of the slot in the tip if you're using flat strokes, or just one side if you're doing arches.

This is great! I have a lot of reading and viewing to do on this rainy day! Thank you!

I found some videos which give a lot of detailed explanations. It's called British Girl Bakes.
https://www.youtube.com/channel/UC1k3PDqnjUG8wMH1vY3yojA