About the Tolls.
There is only 1 top-top on the way in. It's the first toll just after the customs & 3rd from left. Yes, Tambah Nilai. If you miss that, you can buy/top-up the toll @ the building on the left of the 2nd toll before 6/7pm.
Otherwise, you guys can always top up the card @ any Petronas kiosk for 50cents svc charge.
If money runs out & no more top-up? Don't worry, just wait a while & someone will come over to take cash from you.
About driving.
I never keep to the limit which is 110 on most parts. This is the speed where all coaches, trucks & lorries travel. You do not want to be between & behind them. They will overtake you if they find you're slow enough & trust me, these drivers have no qualms to run you over or pull into your lane least expected. Always flash your headlight or put a right signal when you are 50m before passing them on the right or left. If the lanes are clear on the left, you can do as you please but please do not hog the right/1st lane. Most cars that hog are Sg cars & you'll find that Malaysian cars are mostly very considerate.
Be careful @ the stretch after Tangkak towards Melaka. There are canals running under the highway & uneven. Don't drive too fast or you'll "fly".
If someone "accidentally" knocks onto you. DO NOT stop. If anyone claiming to be police & wave to you to stop, DO NOT stop. The polis only comes in white cars with blue/yellow insignias. They are usually Proton Waja or a small jeep with siren box on top.
Get the Plus telephone no & you can call them toll free when you car breaks down etc. They'll send a rescue vehicle in yellow/white pickup with blue lights which may take an hour+/- to come. If you're paranoid, find & note down JB police no as well.
About TP aka Polis.
Best to keep within limits on the 1st 3 tolls & the last 3 for the return leg. They like to nail you there as it's "good business" since most are Sg cars on that stretch of the highway. They have their lunch, tea-break, dinner & especially Friday prayers where it'll be quite fine. You can take the ticket & pay $ later or simply ask them nicely to see how they can help. Take the instructions from there & be obedient. If they're in good mood, they'll even warn you where else there might be road blocks.
Sometimes, even if you don't speed, they will stop you. They seldom conduct road blocks on the NS highway but do have patrols near major towns so be careful.
About Melaka
Most of us visit Melaka for the old town. Look @ the Bandaraya sign but you basically dive straight all the way in then make a few left turns. You'll reach the old town within 15-30 mins on good traffic but can take hour+ when it's bad. @ the old town, You'll see the famous red building on your left with many tourists then make a right turn up the bridge & across the canal to the Chinatown area. I think you can see the OCBC buiilding on the left. You can park by some open carpark lots where they take about RM2-5 or pay metered parking. (They do check & will fine you!) Or make a few rounds around the estate which is not big but remember to U-turn @ the end of the shophouses on your right, if you go straight, you'll head to the beach which is quite nice but no swimming. You can have pony rides & fly kites there.
The pasar malam only comes alive @ night on Fri, Sat & Sun nights till 11+pm & on eve? + public holidays.
The best Portuguese & Peranakan food is not there but on the suburbs.
There's a huge shopping mall further down from the red fort.
Basically, people go there for the culture, food, street life & some museums. The Little Nonya is shot inside the Peranakan Museum on the first street & you need to pay an entrance fee. You can also try the rice ball Chicken rice but a little overhyped IMHO.
Hope the above helps.