What brand of boots to buy? Friends, coaches, fitter will all have recommendations. But you can also post questions on www.skatingforums.com. We get questions over there about wide feet, skater weight, narrow feet, split widths (narrow heels-wide forefoot) all the time. Lots of people eager to share their experiences in answer to your questions.
You'll probably get recommendations for 'beginner boots' from one of the big companies: Jackson and Reidell are widely respected for their beginner skates (with attached beginner blades); these are costly but not expensive. Their ads say they can be used up to single jumps. They will last longer than 'play skates'. Play skates may look like figure skates, but they can also look like tennis shoes. Some people start out with these, but they won't carry you very far if you're serious. I've never heard anyone recommend buying skates from a sporting goods store. If all you want to do is stroke around a few times a year, play skates should be fine. If you want to work towards jumps and spins, then beginner skates is a better bet.
Unless you're really lucky, your first pair of boots will hurt like the devil. Since you have no experience, you won't know what's an acceptable level of discomfort. If the boots fit so badly they actually damage your feet (I had a pair of boots that split a toenail) take them back right away and work with your fitter to get them replaced by a better size.
Your heel should not rise out of the heel of the boot. If the heel is loose but the forefoot of the boot fits fine, you can try a silipos gel tube around the heel. I found heat molding the heel of the boot to make it narrower, never worked for me. I never had a boot heel that was too narrow. I think that can be stretched out with heat molding.
If the forefoot crushes your feet (blistered toes, the forefoot is so narrow you walk in pain after you skate), the skate fitter can help with heat molding. You might be able to return the boots and get better fitting ones if the problem is actually a bad fit on the fitter's part (e.g. having to skate with toes curled to get your feet in the boots). Get advice from a coach about your fit problems if you decide to take this route. (Note: you have to do this right away after you get the boots, don't wait 6 months and expect a refund or a swap). If you can't return the boots and the forefoot pain is crippling, there's an absolutely last ditch desperation (semi-destructive) solution if the forefoot of the boot is too narrow (NOT RECOMMENDED FOR BEGINNERS TO DO ON THEIR OWN). You'll never be able to sell or return your boots if you do this. But if you're thinking of buying new boots because the ones you have now are tearing up your forefeet, hey, it's worth considering. See if you can find a coach to help you out.
Here's the thing about your first pair of boots, it helps to think of them as 'throwaways'. There doesn't seem to be an aftermarket for used adult beginner skates, so you probably can't sell them. Enjoy them, and when you feel you want to move on to new boots, move on. Don't let badly fitting boots destroy your feet because 'the boots still have wear in them'. If you're skating at a higher level than your boots can support, time for new ones. Don't end up with an injury because the boot can't support your ankle on a landing or the blade breaks. Boots are your most important tool from both a safety and health perspective.
Ready to skate more, but your boots are holding you back? Move on.
Well, you'll go through similar steps in picking boot 2 and maybe boot 3. But by the time you get to boots 4 (!!) you'll have enough knowledge to pick them (and the blades) out yourself. Good Luck!