There's oil in them engines

Hey folks, I am going to ferrying an airplane from Florida to Virginia next
week. This airplane has a Lycoming O-360 and is now using 100 weight oil.
The airplane is going to stay in Virginia for several months.

Question 1:

To the pilots that fly in this, or similar areas, would you recommend
switching to a multiweight oil? I've asked two mechanics, one said that I
should definitely switch the oil and the other said that 100 weight would be
fine and that I would have to just let the engine warm up longer.

Question 2:

If the answer to the above question is to change the oil, should I have it
changed before the trip up from Florida, or wait until I'm here in Virginia?

Question 3:

Where is a good place to buy oil online or somewhere in Virginia? I can't
seem to locate an oil distributor in Virginia that will sell aviation oil by
the case to individuals. I've looked into the usual on-line culprits,
Aircraft Spruce, Chief, etc. They seem to be about the same price.

Question 4:

Okay, this one is only sorta oil related. Should I look into a preheater?
The airplane will be housed in a non-heated hangar. If you think
pre-heating is necessary for the Virginia winter weather, should it be just
a sump heater or should I get the core heater too?

Thank you for your informative inputs.