1. 'I (hereby) attach...' is a formal set expression; ''I am attaching" is informal.
2. I am sending... (even formally, the present simple is not used here)
3. & 4: both possible, since the action in question may reasonably be viewed from either a general (simple) or an ongoing (progressive) standpoint. Probably, however, a natural tendency toward verbal concord would make 'clean' slightly more idiomatic that 'are cleaning' in (3).
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