Might actually be a good fit on that line.

You're technically 2 players short with no money, So moves would need to be made. A 20 man roster isn't cap compliant.

Leafs have been running 20 men for like 2 years now. Other teams have run as few as 19 (and I thought I even saw 18 once) at times. A 20 man roster is absolutely fine, especially with the Marlies in Toronto available for call-ups. They literally just walk to the next pad over in the practice rink the morning of when they need a call up. No biggie.

That works for a few days maybe or if someone ends up on LTIR, but you have to have cap space available to call players up. Pens(JR) screwed up a couple years ago and had to finish the season with 5 Dmen because we had no space left to bring someone from WBS. Cutting it that close you risk playing games with a less than full roster. Not to mention that unless Kerfoot and Holl suddenly develop "Hossa allergies", they won't be on LTIR lol

There’s no cap space for a call-up, unless someone goes on LTIR.

Okay? So worst case you play a game or two down a man. Big deal some teams did it before without issue. I will remind you we have been doing this for nearly 2 years already and our biggest crisis was having to have a emergency goalie as a backup once (and he never saw the ice obv). In almost every realistic case the guy can go on LTIR no problem and this is never an issue.
And I presume in this particular case Kerf and Holl being on LTIR is just as a trade without a trade proposal, but I'm not OP so I can't tell you what he was thinking there. Either way they are both positive value players and can be moved no issue so again I don't see any problem here.

He’s old, slow and not that great anymore, at the most I’d put him as my 4th line guy

He's never really been the fastest but I guess he wouldn't be the one to go fetch the puck if he's slower and would kind of take up Tavares space since the only thing he would be able to do is crash the net.

I imagine that instead of having this never ending debate on whether or not Holl and Kerfoot have value (they do), the OP just slapped them on the LTIR assuming that they would be moved.

Also Is injury prone

This is correct I put them ltir for this exact reason just was focusing on the main trade