Does the car consume coolant other than by visible leakage?

Does the oil look like a chocolate shake? If so, then you've probably have head/block problem that allows coolant to get in oil.

Oil in coolant? Similar scenario just opposite case.

Oil is visible on outside of cylinder head? At mating seam w/block, or higher up? might only be valve cover gasket, or damaged breather tube.

Rough running and hesitation could indicate an intake leak somewhere that allows unmetered air into engine. Typical problems, intake duct downstream of airflow meter, vacuum lines, breather hose, oil filler or dipstick or injector o-rings.

Running hot might indicate a faulty thermostate, improper water/coolant ratio, weak water pump or ignition related problems effecting engine timing. A lean running engine (air leaks) will also run hot.

Have you pulled the spark plugs? If one or more look especially clean, could indicate coolant leak via headgasket or head into combustion chamber resulting in "steamcleaning" of plugs.

How about exhaust, have noticed vapors after initial system warm up or white smoke. Does exhaust smell like coolant?

It might be wise to have a pressure leakdown test done by a reputable shop prior to concluding major internal problems.

Do you own a shop manual? The Bentley book is extremely useful and can be had for around $50 at larger bookstores, Amazon.com, or even on Ebay sometimes for less. For about an hours worth of labor, it is a steal. Even if you don't plan to work on your own car, it is worth buying to educate yourself about how it works. A knowlegable consumer is less likely to take it in the shorts from repair shops than one who isn't.
If you plan on keeping a 14+ year old car running without spending a fortune, you might what to learn to DIY. Good Luck!