Just a few things to consider and ask yourself before you start dropping $$ into your system!
How many sets of RCA pre outs are on the back of your Alpine Head unit that you have?
How many speakers do you plan to run with the importance being the size of the front speakers you can fit? If you are fortunate to have 6.5 holes cut up front or in the doors you are ahead of the game in the sound quality that you can produce! If not you need to decide if you are willing to cut holes in your kick panels or doors to accommodate this size of speaker?
If not you are than limiting yourself to 4 in coaxial or 4x6 speakers up front which will be your limiting factor in sound quality! So buying a big 4 channel amp would not be in your interest to power the 4 inch speakers as they are severely limited on RMS power and sound reproduction. Just something one must take into consideration on their build.
If plans are to add a sub or set of subs than in most cases you are better off looking at a separate amp for these unless you go for a 5 channel amp? Again take into consideration the RMS power rating on the amp and matching it to the speaker RMS. I would recommend a sub with at least 300w of RMS and amp that matches this output as starter.
Having said this you must be aware that your ‘alternator” that you have is capable of supplying the necessary charge to run your system in addition to the accessories you have installed presently. It may run things presently, A/C electric fans, lights, etc but may not be capable of handling the extra amps from your new amps. You than have the added expense of purchasing a new alternator to keep up which many overlook! The upgrade is going to suck another 35 amps – 60 amps so if you have a 60 amp alternator it will not cut it. It is best to go to a CS 140 amp alternator and forget about the 100 amp alternator.
In doing this you will need to run 4 gauge wire minimum from alternator to battery to handle the extra charging. 1 gauge from battery to starter and 1 gauge from negative to engine block is a good idea. Add minimum 4 gauge from negative battery to radiator ground. Get good quality wire not aluminum clad wiring that is being sold by all the brand name suppliers because of cost.
These folks have the best quality Power, speaker and RCA cables and will take all the guess work out of one’s install. http://www.knukonceptz.com/index.cfm
They offer complete install kits also.
How much power? 80-100w RMS out of an amp is a good place to be. 270-300w for a single 10 inch sub is also good. Just be aware on mating the sub impedance with the amps (2 or 4 ohm).
Jl audio makes a great 5 channel amp that is small Powerful and will fit under the front seat, although I would prefer to mount amp in trunk as there is more air flow. Alpine has some good amplifiers PDX series but are a class D which are better suited for subs. They also have a small foot print.
Kicker amps work very well also although larger and take up space.
Speakers: These you really need to hear for yourself! The POLK DB series are a great starting point from the sound quality and price. If you can find a set of their MOMO 6x9 they are great! Just these in the back package tray alone Sound impressive with 80-100w rms running to them. These were their high end speakers worth every penny. 100.00-125.00 and can handle 125w rms each. They need a minimum of 60w to sound decent. The same can be said for their 6.5 components Momos if you can scoop them on eBay. 150.00. 175.00 new 6500 series.
There DB series is a step down but there new MM line replaces the MOMOS but is not quite as good as there older MOMO lines that can still be found on eBay.
Audison makes a good speaker. Their hertz high energy line sound very good.
Key is to take the time required to match your components properly and be realistic with your expectations and your sound system will meet them. Take your time in planning and installing to save costly mistakes!