Voltage regulator, starter, fuel pressure? HELP

Decided to buy this 98 Suburban from my step-sister a couple of weeks ago.  It had been in her driveway for a while (she has a newer one now).  Before I picked it up, they replaced the power steering pump and smogged.  Initially failed smog because the computer needed to reset after the battery had gone dead.  Passed smog after being driven for a bit.  About a week later I went to start and it just turned over and didn't start.  As if it were out of gas.  I killed the battery trying to start it.  A neighbor gave me a jump and I went to the gas station and filled up.  Figuring the battery would recharge driving I ended up at a drive-thru.  It died in the drive through.  Luckily it was next to an O'Reilly's.  While the battery was dead the guy was checking but we couldn't turn over because there wasn't enough charge so he had me honk my horn.  He said it's probably the voltage regulator.  I bought a new battery and drove home.  Since then I've driven it very short distances (1/2 mile or less) and have noticed a couple of things.  The voltage on the dash doesn't seem too irregular.  But, if I let it sit without driving for a day, it is hard to start.  In fact, it kind of pauses while turning over at times.  Is that the voltage regulator or some other issue?

Also, there is a knock that is more prevalent when it's cold and kind of subsides as it warms.  There's also a weird whining or high pitched hum coming from the engine as well and a grinding type sound coming from behind the passenger side dash (I could be slightly paranoid about the noises at this point).

Did I buy a clunker???  Am I going to go broke trying to fix it?  WTH is even wrong!  I have bad car karma and would love to just fix it to the point where I don't have to worry.  Could much of this be alleviated with a tune up?

Thanks in advance!!!