First off, spread eagles are not easy to learn, but you will get it! Keep working on it, and you'll get there in time.
Now, each of your questions in order:
1. You want to keep your weight even between both feet, and slightly towards the heel of each blade once you are fully in position. The most common mistake skaters make entering a spread eagle from back crossovers is to not "trust" the leading foot they are stepping to when they begin the actual spread eagle, keeping their weight over the back foot. If they are starting from a forward outside edge, the common error is not to "trust" the back outside edge back foot they just placed down. The key either way is to try to commit to the position right away, or the edge(s) run away from you.
2. I like to go from back crossovers, stepping from a back outside edge onto a forward outside edge with the leading foot of the actual spread eagle, shifting my weight to immediately place it evenly between both feet. I also know skaters who prefer starting from a forward outside edge, swinging the free foot back to place it on the back outside edge for the spread eagle. Try both entries and see what one works best for you - once you get comfortable on the spread eagle doing either entry, you'll be able to pick up the other pretty easily.
Another option you might want to try if you can do an inside spread eagle is to try to go from a forward inside spread eagle to a straight line, and then roll over to the outside edge. Just think of flattening out the curve of the inside spread eagle, find your straight line, and then tip your leading foot ankle to the outside edge gradually to shift the curve. Again, if you can get the outside spread eagle position comfortable, you'll be able to get the other entries more easily.
3. Whatever feels comfortable for arms is fine. You might want to just leave them out at first until you get comfortable (make sure you aren't rounding your shoulders forward, keep them open like you're trying to stretch your chest upwards and outwards), but once you can do the spread eagle, experiment as much as you can! There are many gorgeous things you can do with your arms on a spread eagle - take a look at what other skaters do, and give their positions a try. Don't be afraid to play with it - remember, skating is fun and creative!
4. Other tips...oh man, I could write a book on other tips.
- Once you get on the outside edge, think of relaxing the front of your hips and pushing them slightly forward, to make sure you don't look "bent over" the spread eagle, but are holding your body straight and upright.
- Don't try to lean backwards - the beautiful backwards lean it looks like is happening is caused by the speed you are skating at and the depth of your curve (centripetal force if you want the physics term). Just think of holding your body as straight as possible, and let your skating and edges do the rest.
- You can stretch your turnout by doing the "frog position" off ice. It is, unfortunately, an uncomfortable and slow stretch, but it does wonders for getting good turnout through your hips (where it should happen from, not your feet or knees). In the "sources", I've included a link to a photo of someone doing the frog position to give you a visual, but you want to lay on your stomach on the floor, and make sure your hips are pressed down flat to the floor (it can be really uncomfortable to keep your back arched if you support yourself on your elbows, so I recommend just staying down). You want to slide your knees on the floor up towards your shoulders as far as you can go - and you will probably notice your feet can't stay on the floor when you do this. Put the soles of your feet together, keeping your hips and knees on the floor. The key is to STAY THERE for as long as you can stand it - I often have my students do this stretch for 5 minutes a day after warming up. Gravity helps pull your feet towards the floor, and in time you will notice your turnout improving. It is much more comfortable to do this on a yoga mat than on a bare floor, but doing it on too soft of a surface won't help your stretch very much at all. If it hurts your knees, you can do the same stretch on your back, putting the soles of your feet together the same way and taking the same basic position, but letting your knees drop to the floor instead of your feet. Less painful, but it takes a bit longer to get the same amount of turnout this way. (Wow, that was practically a book right there!)
- The last tip I have is to work on your spread eagles after you are really well warmed up, as doing them cold can often lead to muscle pulls, which are definitely not fun. At the rink I teach at, many of the skaters working on spread eagles use the last 5-10 minutes of the session they skate to work on them, after they have been skating for a while and are significantly warmed up.
I hope all this information helps, and good luck with your spread eagle!