That's a lot of ground to cover in 17-18 days. Keep in mind that at least 3 of these destinations are islands that you will have to either fly to or reach by boat. I would eliminate at least 2 destinations to make the itinerary more manageable. I have only been to Singapore, Penang and Langkawi: use public transportation or taxis in Singapore; in Penang, you can walk or take a taxi in Georgetown but a car and driver will be necessary to tour the island; on Langkawi it is easy to rent a car and self-drive.

I agree with Craig, cut a destination or two. You haven't figured in travel time, so while you might think you have a whole day at Genting, you have an overnight and a couple of hours in the evening and the morning.

Options ofr intransport include luxury buses, for instance from Singapore to Malacca and Malacca to KL. I know there is a luxury bus from KL to Penang, I don't know about a stop in the Highlands.

In Penang, stay in Georgetown. Persoanlly, I wouldn't bother touring the island. In Georgetown you can walk, take taxis or bicycle rickshaws.

You don't need a guide in any of these places.

Vegetarian food should be easy to find.

I would also consider cutting out Genting from your list. Apart from slightly run-down casinos and dysfunctional theme park, there is really nothing up there. Spend the extra day in Langkawi.

Also re: vegetarian food, try any Indian restaurant, they usually have a good South-Indian-style vegetarian food available. If you can find any Chinese restaurants that are run by Buddhist monks or temples, they are a fantastic and tasty alternative as well.

Be careful of asking for vegetarian in regular Chinese places - they may still add fish/prawn stock or oyster sauce etc. Otherwise they may over-dose on the MSG or use "mock meats" which are quite freaky.

Genting Highlands is a bore uless you want to gamble, and further there is a beautiful 2 tear olsd lovely casino inj Sinci in Sigaore, Singaporeb is a stretch for more that 2 full dats, You shpould have ataxi with youroarentsb unless they do not mind walking a mike and stabdung a but, But taxis are inexppensive.,If you enjoy Chinese foodm though a pricy the Raffles Restarabnt of the same name is one of th best I have eaten at. Though it involves walking I suggest 1.2 mike in LittleUndia tgi get very difference.Most of the shopping, and it is high-end- is down town in a 4 block area but the prices are equak or more than the US but are cutting edge.
I would hire a guide/drive for an outing to the Cameron Highlands but check the weath first. When we went in March it was lovely with hundreds of acreas of tea planttions and rose and vegeabablebplantsfes, Mije just wants visitsors to see the Toconic Mouutins. It is a full day outing and better to make the long drive, A visit to th Petronas 5ower is worth it but get there by 8AN in a week day to avoid a long wait. Penang is quite lovely but I check the rainfall there at that time of year. We eat. I would sat a max, is more than sufficent to get you through KL.