A proposal is a sales document, not an informational document. Include the necessary information, but make it persuasive.
When writing proposals, say what needs to be said. No more. You can say more if you want, but it just makes your proposal longer and less likely to be read.
Reacting to RFPs doesn’t work. If you don’t have a relationship with the client before the RFP is issued, it is unlikely you are going to win.
If you add just one more comma at the end of a list, you will make your writing clearer.
You should always include a cover letter when you send a proposal. It’s good business etiquette, it’s polite, and there’s no reason not to.