Using HDPE/poly pipe is the best IMO. The pipe is flexible, so it can make slight bends and turns to fit. For the connectors use Hansen or Buteline ones. Very reliable. But do note that you will have to use SIRIM certified pipes if you want to use Hansen or Buteline connections, as the internal diameter of the pipe is important. If you want to use the "O" ring Poly connectors you don't have to use SIRIM pipe, as only the outer diameter of the pipe is important. SIRIM certified pipes have a pressure rating, meaning the pipe wall thickness is specified.

You can run the pipe along the wall/fence, up the front of the house, and into the ceiling to the water tank. There, you need to make a branch off to the kitchen, probably out the back roof, and down the back wall of the house. The pipe size is the actual outside diameter of pipe, so you can judge the size should you need to make any holes for the pipe to go through.

The size of pipe should be 25 mm or larger. But I don't think larger than 25 mm is necessary, as the water meter inlet/outlet is 1/2 inch. So no point going extremely large for this incoming pipe. The branch off to the kitchen can be 20 mm pipe and is more than enough for the kitchen tap. You could save some headache by just going for 25 mm pipe all the way. One 100 m roll of 25 mm SIRIM poly pipe costs under RM 200.

If you want to DIY the Hansen connectors are suitable, because you only need a spanner to tighten the nut. Buteline connectors are excellent and permanently leak free, but you do need special crimpers for it. Each size of crimper costs more than RM 200, and you need to have the correct sizes for each pipe you use. Rough price for Hansen is about RM 3/connector, and RM 4/connector for Buteline. Cutting poly pipe only needs simple tools, about RM 15 from any hardware shop.

Changing this incoming pipe to your water tank is well within the ability of anyone with reasonable skill. You should attempt it if this describes you.