Help please.Replacing cast iron soil stack or cheaper alternative

Hi everyone,
First time poster.I wish to redo my bathroom and was wondering if anyone could guide me how to best proceed.

1.Want to add close coupled toilet with enclosed sides.The current one has a 90 degree connector to the iron one in the ground under floorboards.Is this ok to connect to new one or does it need replacing.

2.The waste from sink and bath tub goes to an open hopper.I wish to connect this to the soil stack,as need to get rid of bath and install a shower enclosure.

What would be the easiest way to connect the waste from sink and new shower enclosure,into the cast iron soil stack.Do i need to replace the whole lot or can i get some long term cheaper alternative.

Thanks.

 

Thank you guys.Would you be kind enough to guide me to a link or a step by step connection guide.I am happy to buy all parts and hopefully able to tackle the job myself.How much roughly am i looking at for the whole stack.

Can i leave the bottom bit intact (which is in concrete and goes to IC)and cut just few inches above the ground and use a connection to connect the whole stact.

 

thanks a lot guy. very helpful link. finally how do i route shower waste under floorboards. cannot change the layout.

At present the waste pipes are hidden under the bath sitting directly on floor. the joists are running in the other direction. the pipe will need to go across by 3 metre to the wall.