without going through all possible options (google can help there) why do you have the copy job on Windows Schedule instead of a SQL server job? 
It would be better...

if just moving the accounts to another OU within the same Domain it will not change the account SID so your servers will not be impacted.

openquery with truncate may work - if not create a stored proc on oracle that does the truncate for you and exec it through openquery

in the project file 
<DtsPackage FormatVersion="8">
in the package itself
DTS:LastModifiedProductVersion="15.0.0900.40"
  DTS:Name="PackageFormatVersion">8</DTS:Property>

this is with
Microsoft Visual Studio Professional 2017 Version 15.9.6
SQL Server Data Tools 15.1.61901.03220

possibly not the answer you wish for but what have you researched so far?

100 measures is not much - one of my "cubes" has 22 dimensions, 1 fact...

for tempdb there is nothing you can do.

if however you are also talking about having all permanent tables of a user on their own file(s) then it is...

did you try the index and the insert into a temp table as I suggested?
If so what were the results

look at https://support.microsoft.com/en-us/help/918992/how-to-transfer-logins-and-passwords-between-instances-of-sql-server
contains code for both functions.

you may also wish to look at https://dbatools.io/ for other tools to do this (and a lot more)

missing index as per explain plan might help a bit there.

you could try changing the index to IX_PROPERTY__SOURCE_ID be as follows

create nonclustered index IX_PROPERTY__SOURCE_ID...

SSAS tabular only works with Windows authentication. So if the server is indeed in Tabular mode you need to try it that way.