The cover letter has most everything you want. You can edit and customize, but as it is when installed should have most of what  you  want. 

Settings > Client Letter will present you with the ability to edit the paragraphs of the letter. The process is clunky, but doable with patience.

Settings > Options > Items to print is where you lay out print order and what  you want to include. e.g. Client Copy - I include worksheets and depreciation schedules. Government Copy I put invoice on top, followed federal and state estimates and the 8879 forms for e-file (or full return if mailing, but that is real rare)

I do not use Slip sheets. I have personally found them of little use, as the client letter contains everything. For the 1040 you can make entries in Screen 47 - Letter Misc 1 will make an opening statement on the client letter and Letter Misc 2 will make a closing statement. PRESS F1 to get

Add notes to a tax return

1. Click the Detail tab.

2. At the Contents tab, click the Notes screen.

3. To create a new note, select the type of note under Print As, and then click Add.

   Worksheet Notes print before the tax return in Supplemental Information.

   Statement Notes print after the tax return in Supplemental Information.

   Letter Misc 1 and 2 Notes print as opening and closing paragraphs on the Client Letter. The program assigns the text you type to the  [MISC1] and [MISC2] keywords.

   (1065, 1120S, 1041) Schedule K-1 Notes print as supplemental information for each partner's, shareholder's, or beneficiary's Schedule K-1. The program assigns the text you type to the [SCHK1] keyword for the Client Letter.

To edit an existing note, click the note in the list on the left.

4. Click the Spell Check button to check the spelling of the note.

NOTES:
If you add a note for Letter Misc 1 and Misc 2, you can format the font and alignment of the note text using the toolbar at the top of the note.

Use the font lists and the buttons on the toolbar to format the notes.