Sounds right, every e-visa can only be applied for from a country you are currently in, so if you are using the malysian site, you have to prove you are there, it will be the same for other countries. They don't neccessarily ask for a copy of the stamp, but they will ask for some evidence.
If you've already done 180 days here on exempt, its definetly going to raise an eyebrow, you could apply for a tourist visa while in vietnam. Follow James Millers advice and have the 3 peices of info/money.
Yes there is parking on the side of the roads in the site and several car parks, but you can't 'change' passports there or did you mean transfer your stamps?
if you don't get the non o in your country, and fly in exempt, you will also have to buy an onward ticket as well as paying an agent to purely help open a bank account.
you will have to employ an agent to open a bank account for you, which will need to be seeded for 2 months with 800k before you apply for non o in country. Cut the agent out of this part of the process and do it before you leave, using 800k in your home country account.
Step 1 get your non O via e-visa from your local embassy before you leave. Step organise your initial stay before you leave, (a seviced apartment might be best, like a hotel bbut designed for longer lets and has all the comforts of an apartment. Step 3 visit Imigration get a resients certificate and open a bank account. Step 4 with a letting agent ( or without find a condo).