Burnt rubber smell from under hood passenger side-worth it?Pay for work or sell and buy another?

1.)Depending on how long I've driven or stops made for that day when I come to my
destination and park, burnt rubber smell steams out from under hood into the direction of
passenger side. It' s been 4 months now. I'm worried that it's costly. But I need to know if
it's dangerous. My boyfriend who's a mechanic doesn't have the patience to communicate to
me in a way that I understand without feeling like I don't trust his opinion. He told me it's
safe. I don't feel safe. Of course, I haven't taken it to get looked at because of financial
issues.. Any advice would be greatly appreciated.
*the smoke is isn't anywhere near how an overheated car gets. It's more like the smoke
from the aftermath of putting out a bonfire. Breezy but smells like burnt rubber.

2.) Minimal oil leak from under the car where the hood is. Noticed around same time burnt oil
smell. - Will this be costly to repair?

3.) Oil changes: I was charged $15 extra because "they have to remove the plastic "shield" from
where the oil filter and oil was to be drained. Is this true?

4.) The wheels or rims, not sure what they're called, missing 2 of the "caps" or "cones" that's
placed in the center of the silver "rim" where the tire is surrounding. Would it throw the
car out of balance if when the tires are rotated the two remaining the "cones" are on one
side? Or should be it one on each side?

5.) Last week I started noticing a faint "shhhhhh-rattle" sound from where my front dash is.
where the cd/cassette player and vents are. Is this an indication of something is wrong?
any ideas what?

6.) Time belt/chain hasn't been replaced. Presently the car is at 191,100 miles. How would I
know I if it was replaced/ serviced? Should I get it done? Is this costly?

* had just purchased car from the original owner 4 months prior. They "promised" car was
mechanically in good shape. My bf came with me and he examined car but withheld his
findings from me until a month later and told me I bought a lemon.

* my xterra does not have a sun/moon roof. Not sure what model: SE/XE. It came with single
cd/cassette player. I would have to consult my manuel but im in bed it's midnight. Parked
outside :(

Thank you so very much. :)