As far as the questions;
2) No. Or that is, I'm going to assume here that you'll be flying back to Macedonia. Any and all flights that are international are a "no go" as far as
DCL check in goes. It's the end destination that counts for this on your itinerary, so if you're connecting in Atlanta or NewArk for instance onto a EU-bound flight, it is still considered an international flight. You will have to check your bagage yourself.
1) I would never play that gamble with a transatlantic flight personally. Normally it should be a doable time, but it does not really leave you any wiggleroom for any bumps down the road. To give you an idea; after our last cruise we were scheduled on a 3 pm flight, sure we'ld make that one but aiming for the 12am one as a standby as we knew the 2 pm often is delayed and could mean not making our connecting flight to AMS at EWR. We were amongst the first off board. First to find our bags, one of the first busses to MCO. While we were last off the bus (wheelchair procedure

), we were in the same check in line as those on our bus. We did make the 11 am flight (yep 11 am, they expected lots of problems later that day and wanted as much folks out asap), but they ended up holding the flight for us! The time it took? About 20 minutes to get my powerchair checked and than a faster than speed of light trip through security and to the gate. Sometimes needing assistance pays of in getting somewhere quickly. That was with everything going our way, getting FOTL at MCO everywhere and everything going nice and dandy with DCL. Smart move by the way, weather indeed would've left us missing the connection on our scheduled MCO-EWR flight.
For 12.30 it basically only takes "that" for you to either miss you first flight or at least be very nervous about possibily not getting to MCO and the gate in time. No biggie for those US-flights, but if you have a connection to make to the EU..... different story. Most airports tend to not get serviced with multiple flights per day per airline. Which would mean being delayed for at least one day at either MCO or your connecting airport. I never sweat a possible not being on time for a US-flight but transatlantic (either way) is a different animal IMHO. If at all possible, I'ld go for a later departure time. With most airlines you can do a free standby if that turns out to suit your likings better and you do arrive at the airport early enough (like we did).
If not, I'ld stick with DCL transport. They also book some flights out early (too early if anything does go oops) and do their best to get you on the first busses departing if you inform them about needing to make an early flight. With rental, you'ld have to go to get the car, deal with the luggage after that, drop off one person at airport with luggage, bring back car, do that paperwork, check in etc. etc. DCL transfers run smoothly when they get going and should be no slower if not quicker than having to deal with the rental company. It would mean you having to be ok with "handing over control" and if something happens sweat it out and hand your faith over to the DCL gods. On the other hand, that would mean not being behind the wheel if it does come close which also can be a blessing.