Hi,
To start, here is a link to
Crutchfield and what fits your vehicle.
Find what fits your car - Crutchfield
You can do a lot depending on your budget. You don't state a budget so we have no real starting point.
In my opinion you get what you pay for...if you want a quality head unit you are going to have to spend a few hundred bucks...want navigation you're going to have to spend more...You can get a decent Pioneer for around $300.00, no nav. I suggest buying the well known, good quality brands...Pioneer, Alpine, etc. Stay away from the cheap units/brands as they aren't well made and often wind up with problems.
A good head unit is going to provide quality sound...but if you play them through 13 year old factory speakers you are losing out on that quality sound...I suggest a decent pair of coaxial speakers for the front doors. You can run a nice pair of coaxials off of the head unit's amp but they won't get "good" loud, just loud and perhaps noisy, depends on the speaker and head unit. If you want a bit loud add a small amp especially if you want a nice pair of component speakers, which are my preferred speaker for the front doors. If you have factory rear speakers leave them alone...
you're going to have to do your homework reading about the different head units...when you have a selection of 3 to 5 you will be better prepared to ask good questions.
Speakers are more difficult as we all have our preferences...I suggest going to a couple of local shops and listening to them to again whittle down the choices to several.
Don't forget you will need a dash kit, possibly an antenna adapter, harnesses, connectors, etc. if you are doing it yourself...if a shop is going to do it they will know what is needed you just have to add the cost to your budget.
Don't forget your mobile phone...whether Android or Apple may make a difference...
Good luck and keep us informed.