ILLUSTRATOR FILES INTO INDESIGN HELP

While InDesign would be the better choice for future projects, using it for your current project is not absolutely necessary. Save all of your Illustrator files as PDFs (Illustrator default settings) then combine them in Acrobat. To reduce the file size, save-as an optimized PDF from Acrobat, where you have good control over compression and downsampling settings and the size reduction is very good, particularly when you discard unnecessary information. If you make changes to one page, you can use Acrobat to replace the page in your existing combined PDF.

Unless there’s a need to build all of this in Illustrator I’d suggest doing complex layouts in InDesign from the start. That being said, it’s all of the embedded items that are adding to the bulk of your file sizes. You could:

A.) Make PDFs of the Illustrator artboards and import the PDFs into InDesign. This might (probably would) reduce your overall file size as   the placed elements will be optimized during the process of making the PDFs. This will limit later editability though.

B.) Remove the embedded elements if possible and re-place them separately into InDesign along with the placed Illustrator files. By linking the images and PDFs that are currently embedded in Illustrator directly to InDesign you’ll have a more efficient document build.

C.) Make PDFs from Illustrator then use a 3rd Party plugin like PDF2ID to convert everything over to a native InDesign document.

Reducing the file size might get tricky.

Raster images can be compressed well in InDesign. But you will of course lose image quality the more you compress.

With vector content that might get difficult. When there are many objects and/or many ancho points, the file won't get smaller.

Many anchor points can typically be found in CAD files or when you convert type to paths.

As for the master page: yes you can do that in InDesign. But I'm not sure about the specific nature of your question. What is it you want to do exactly?