Several new issues with my 99 volvo s8 has 285k

Recently moved to Texas...driving more than usual on my 99 Volvo S80 -
which has 285K. Love this car! It  always ran great until recently giving me a
hard start - both cold and hot.  Engine sounds louder than normal and feels
(gas pedal) a little rougher.

I've had to change out the ignition coils in the past and thought these may be
an issue - haven't done that yet or replaced the spark plugs either...it does
act like it's not firing on all plugs.

I've also been having to add antifreeze to my overflow every other day...now
every, the last couple of months, too. Initially thought this was because of the
excessive driving and "heat" of the area. Although my temp. gauge hasn't
indicated any sort of overheating.

Thanks in advance for your insight