I hate to sound negative here, especially to someone starting out. Don't get discouraged by what I say , as there is always an exception to the rule.
A 2x4 or the like is probably the worst choice for what you are doing. Spruce /Fir /Pine are on the bottom of the list of bow woods to begin with. Couple that with a moisture content of 15% (approx.) and severe violation of knots and less than ideal handleing of the wood from the time it is cut as a tree, and you are setting yourself up for disappointment and frustration ( totaly the wood and not because of your skills.) I'd hate to see you give up ,thinking it's beyond you ,when I know you can do it with the proper piece of wood.
As a side note, construction grade lumber gets dipped in a chemical bath at the mill (fungicide and pesticide) that you probably don't want to expose your lungs to any more than necessary. It's recommended that you don't burn it and wear a mask when cutting it (not that that ever happens) . Just giving the info here. You do with it what you want.
The cracking sound you hear is likely from the knots. I would be amazed if any kind of backing would keep that in tact. The rawhide would only keep pieces from flying all about when this one blows.
You mentioned cutting some trees as well. This is a great way to make a bow,...................... If you know what you are doing. It's not just a matter of chopping it down and shaping it into a bow. You have to know what you are looking for in a tree. Hidden insect damage ,knots ,spiral grain, disease, etc,etc,etc, will all make a tree worth more to everyone left standing, than cut down and turned into a failed bow. Consider the amount of time a tree has taken to grow to that size and endeavor to craft something that will last at least that long . It doesn't always work out that way but it makes you think long enough that you will pass on something that doesn't really suit your needs. After you cut it(assuming you didn't incorporate any damage due to improper felling) It then needs to be split (maybe) and seasoned properly ,so it doesn't mould, crack , check etc. This could take a few months or a few years.
IMHO your best bet would be to get 1x2 board (Oak,Maple,Ash, Hickory) with nice straight grain, and check out the build along that "Bubby" has on this site or check out GeorgeTsoukala's website which can also be found through this site. A little more time on research will payoff greatly with time not wasted with the wrong board. Best of luck !Looking forward to seeing that first bow.
P.S. it never hurts to find a mentor in your area that you can talk to face to face. Saves a lot of time typing.