1. Renovate the back of the house until the back wall about 6 feet ( I know there is a setback but I understand that it is allowed for this taman as many have renovated to the wall). So an additional 120 sqft.

Usually it is allowed, most setback requirements can be easily found through local authority website and doesn't differ much but do not assume that if your neighbour does it, it is allowed.

2. Extend to the side about 12 x 35 both upstairs and downstairs which means an additional 840sft built up

Again, the setback is at play here, depending on the road you are facing, whether it is considered main road or secondary road, the setback distance differs but usually there should be some rooms to add to the side.

3 As part of the extension, the downstairs bathroom will be extended and reconfigured to add an enclosed shower and a japanese style toilet and a laundry room will be added next to the bathroom. The kitchen will also be relocated and new cabinets and an island be built. An L shape bifold sliding door will be added to allow access to the garden from the dining area.

No constraints here except budget.

4. On the second floor, would like to add a bathroom with a bathtub and a large bedroom with a walk in closet. The layout upstairs will be reconfigured with 2 bedrooms and 1 bathroom being extended as well. After renovation the house will have 5 bedrooms 4 bathrooms and 1 laundry room.

Should be able to do it depending on size of rooms.

5. A small driveway allowing me to drive through one gate and exit another at the side of the house.

I could be wrong but I am pretty certain that this is a nono. I am working based on assumption as you did not mention whether your unit is a bungalow or semi-d but in both cases, I doubt this can be achieved. Entry and exit for "taman" residential type typically allocated towards one road only.

My queries:-

a. With so much change in the layout will a budget of RM200K be sufficient?

To be honest, the layout change is possible with that budget but your fitouts i.e. carpentry, sanitary fittings may be insufficient.

b. Do I need an architect?

Yes, it is recommended to use a professional architect but there are alternatives such as runner (experience on this varies from person to person). Anyone who tells you that you can renovate as long as neighbour doesn't complain should be avoided. The price you pay for renovating without endorsement and CCC far exceeds the cost you save from renovating illegally. Just a simple example that you may be fined if your neighbour does complain, and you will ordered to stop work and go through the legal channels to continue. On top of that, i cannot emphasis enough on the importance of obtaining CCC these days.

c. Will such a driveway with another entrance/exit be allowed?

As above

I PM-ed you a few days back with my contact, feel free to contact me if you have any other questions.

Ok if that's the case i am pretty sure the side exit will not be allowed based on the typology as well as previous experiences with KL and Selangor local council.

Typical terrace house renovation usually ranges from 150-250k so you are not far off. For a better gauge of pricing, it is best to get a cost estimate in order to prepare your planning.

Cheers.