Hey @nayakhaan,
welcome to the community and congrats on thinking about moving your website to HubSpot.
As a HubSpot CMS developer I can say - you can implement almost every external tool and use it in the page-builder with so-called custom modules. Custom modules are not required to create custom code but they will provide you a lot flexibility.
Depending on the tier of HubSpot you’re considering to get you can get quite deep.
For instance - creating custom themes(the “environment” that contains all your templates and modules in your brand-guidelines) and modules are possible from the starter version of things. Maybe even in the free version - haven’t checked it for quite a while.
If you get the Starter version(I’m thinking of the whole suite which contains marketing, sales, service, cms…) you can create quite everything to your needs code wise.
With the Professional version, you get the membership and HubDB functions. Both are really amazing tools. With memberships you can create whole membership pages & experiences. HubDB can be described as “a graphical” Database which is super easy to handle and only your imagination/creativity is the limit. Create a bunch of (multilevel) pages within the same template? No problem for HubDB. Store content for global editing in HubDB? No problem.
Note: If you create a global custom module, you can also create global editing experience
With the Enterprise version, you get everything in Pro as well as Custom objects and serverless functions(and a lot more things).
Custom objects will let you create custom objects in the CRM and use them for anything you like. You can even create (multilevel) pages with custom objects. Super powerful feature if you like to create personalized/CRM powered experienence.
Serverless functions let you create/run serverless functions and influence the web experience without the need to rely on external scripts.
Also - the HubSpot API is free. So you can create private apps(only for one portal) or public apps(for several portals/marketplace) to sync your app data to HubSpot or vise-versa.
If you have specific questions,
I’m happy to help/guide
best,
Anton