Doubtful on #3. The RDL format will be different too so you're looking at an RS Reports migration here too.
The engins upgrade itself is pretty safe. Start with running Upgrade Advisor against the 2005 instance and address all feedback.
32 to 64 bit has some extra challenges if you're reaching out to external resources from within the engine, e.g. OPENROWSET, Linked Servers, OLE Automation, xp_cmdshell, SQL Agent CmdExec steps, etc.
Are you using SSIS anywhere? There are some 32 to 64 bit challenges there as well.
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