Thank you Khaled! This is exactly what I needed. And thank you hhp for the relevant question. I certainly am concerned about usage of it. The pdf Khaled sent helps so much.

Is this behavior generally out of taste and should be avoided unless necessary? Or is it accepted when used minimally? Should I not use it at all if not for justification? And is a tatweel the same as a kashida? I've never been able to do anything with 'Kashida' in any of the Adobe apps, and I have assumed I just don't have the right font.

The issue is I need to type a bismillah, but it needs to match the font of the body text, and there is is no full bismillah glyph in the font. (Sometimes I see a nice one in the character map of the font I'm using.) But I don't want to add a tatweel if it is considered tacky. It just looks so strange to see a bismillah so short without the calligrapher's tatweel! (And I got the first message wrong. It's between 'sin' and 'mim'.)

Also, the swashes that you see in latin fonts, are those available in Arabic fonts too? I've never seen them. What I mean is a long extension that curls above or below the line...like in 'fi'
في
if the 'yah' extended below the baseline for a longer distance without interrupting the other characters. I realize I'm probably getting into 'call the calligrapher' domain here. Tasmeem in InDesign is nice, but I just can't afford the nicer fonts yet, and what I have doesn't seem to give enough variation in the line.