To find out exactly what size will fit where you want you can go to
Crutchfield and use their "outfit my car" option. This is a handy tool to show what will fit, without significant modification, in the factory locations for speakers and head unit.
While you state you have no budget if you want advice and suggestions you need a starting point otherwise members can quote you a $10000 dollar system or a $750 system and would be a big waste of time and effort as well as confusing.
A basic system for an everyday driver...based on my experiences...would be a good head unit, component speakers in the door panels, a 10" or 12" subwoofer in the trunk and one amp to run the speakers. Forget about the rear speakers unless you must have them. Many, including myself, do not bother with them or use some good quality coaxials and use them only as/when needed.
The average mid sized car can usually accomodate 6 1/2" round component speakers in the doors. That allows the mid range driver in the stock location and the tweeter externally attached to the door panel as close to the mid range as possible. This may not be the prettiest and cleanest install for the tweeter but is the easiest to mount and the least costly in time and money. A good pair of components will cost you around $250 and will give all the clean sound and loud music you or your neighbors can stand.
The sub would be in an appropriate enclosure for its size. Expect to pay somewhere around $200 plus for a modest sub and box.
The amp would be appropriate for the speakers and sub. You don't need tons of power though more is usually always better. The quality of the amp is also very important. You can buy a 1000 watt amp at Wally World for under $100 and you would be throwing your money away. Figure to spend around $300 for a decent quality 4 channel amp, around 75 watts per channel to the fronts and the rears bridged to around 200 or so watts to the sub, to power two front speakers and one sub.
The head unit, as well as the other components, are subject to individual favoritism. Generally Pioneer and Alpine seem to be the most highly regarded though their are a lot of people that also favor JVC. Expect to spend around $250 to $400 for a good head unit with at least 2 pre-outs for the amp and other goodies that people just can't live without.
As you can see the above "basics" I describe will cost you roughly $1000. I have not included the wiring kit...$30 to $60...or a kit to house the head unit, should one be needed. Nor have I included labor, unless you will do it yourself, which is area and shop dependent.
You can certainly spend much, much more and get better sound but this is a good starting point IMO.
There are also other variables including buying gear online and shopping around...you can get some great deals online but as always "buyer beware", buying used gear is always a great way to get great gear at a very good price but once again "buyer beware".
So there you have it. A good system for an every day driver that does not require more than the stock battery and amp or more than average installation.
Good luck and keep us posted.