Planning to some renovation work after staying 10 years..hopefully some sifu can give estimated price for the work

1.Make gate wider by demolishing mailbox - Do I need to buy new gate or there is way to modified it?
2.Relocate from side door to middle door so need to rebuild 2 Windows + security door.
3.Build 2 pillar to support balcony
4.Build roof+extension for 2nd floor room - Previous contractor claim existing kitchen extension can support 2nd floor extension.
5.Re-paint whole house
6.Demolish 2 walls

Hi guys, I have an old double-story house that required full renovation and after reading the posts in LYN, I am a bit confused regarding the Architect, Interior Design, CCC, CF, work permit and etc. Hope can get some advice here.
I met some renovation contractor and has given some simple plan. He said I can go to DBKL/Land Office (forgot which) to buy the standard plan and submit to get the work permit and then after work completed, re-submit the plan to get the Certificate.
It doesn't sound like a proper process so need advice here.

The work.
1. Full knockdown and redo the front gate.
2. Extension of probably 4M at the back
3. Re-design or relocate the ground floor room
4. Re-design or relocate the 1st-floor room
5. Maybe extend 1st-floor master bedroom
6. Re-do all wiring and plumbing

Question:
1. For now, I want to design the house plan first, so I should just get Interior Design to design the house plan first, right?
2. Once I have the design, then I can get the various contractors to provide their quotation?
3. Then get the Architect to draw up a proper plan for submission?

Will post more question later.

Thanks.