Ledger on render?

Hi folks,

Will be moving into a new property soon and already looking at adding 'floor level' decking out the back.

1st Q? Can I place a ledger onto the rendered wall? There is a slight slope, so more secure fixings preferred.

2nd Q? With the downpipe and step in the way, can the board be 'cut to fit?

Excuse the moss. No damp in the house, thankfully.

you seriously need to replace your blocked and leaking drains.

The airbrick needs to be open to airflow.

Haven't moved in yet, so can't touch it.
That is on the list. They are cast iron and do need replaced.