first, go to sonicelectronix.com and create an account. you can add a vehicle into your information so all the products shown on the website say if it is compatible with your vehicle. you should check up on what size speakers you need for your mazda, then you can start your search. it has a lot of different search ques that help you choose what you want, how much power, and how much you are willing to spend. If you're looking for quality at a decent price, id get some alpine products. they make great SQ subs and their speakers are known to be great quality. they also have a few touchscreen headunits, which you said you were interested in.
for subs, i would get a type r 12, or two, depending on how much you are willing to spend and how much bass you want. if you get one, get the mrp-m500 amp. if you get two, get the mrp-m1000.
for door speakers, if you're willing to spend the extra money, go for the type r speakers. get a set of components for the front, and either a set of components for the back or coaxials for the back. if you get type r's, get the mrp-f550. if you want to spend a little bit less, get the type-s door speakers. they don't come in components, so get to sets of the coaxials. you can either get the mrp-f300 amp, or get the ktp-445 power pack to plug directly into your headunit.
headunit wise, there are 7 in the new line that you can choose from. i have no experience with the touchscreen units so i cant help you too much here.
make sure you get a good box for your subwoofer too. if you want to buy a prefab one for cheap, knock yourself out, but know it wont sound NEARLY as good as a custom built one.
also, keep in mind that this is one brand of stuff. this is just a decent base line for what you should get. i am definitely a fan of alpine so i may have some bias, but i think they make great products all around. and when i say like you can get this or this,don't feel like you have to or feel obligated to do so, im just trying to make some reasonable recommendations. anyways, good luck dude! hope you're satisfied with your system.
