Originally Posted by
Vivalasvegas
When we arrive in Singapore (we’ve been there twice before) we’re going to either hire a taxi or fly to KL and have 3 days there at the end of the trip, which was longer than we originally planned. So we’ll be looking to stay in KL instead of the airport and seeing it properly.
I had to read your sentence twice. Taxi from Singapore to KL whilst not unheard of, but it's a rather unusual way to get from Singapore to KL. I don't know how much it'll cost but most likely more than an air ticket if you buy it now. And if you want to save some money, it might be better for you to take a taxi to Johor Bahru and then switch to a Malaysian taxi from Johor Bahru to KL. If you are hiring a private transfer from SG to KL, then that's a bit different.
If I were you, I'd just fly because you don't know how long border crossing can take at the Causeway. I think 3 days in KL is good. If you are worried that you might spend too much time in KL, you can split your journey somewhat halfway in Malacca and spend a night there en route to KL from SG.