First of all, it seems that you are comparing apples to hammers to wristwatches. Webflow, React and Bootstrap are entirely different tools trying to solve entirely different problems. So, with respect, I want to ignore that part of the question and focus on what you probably need as I understand it.
Second; the marketing website and the customer portal are different beasts entirely. They will probably have completely different problems to solve, and those will require completely different tools.
Third; as I understand from your explanation, it is yet too early to decide on a tech stack for the systems you want to build. You have some goals in mind, but those must first turn into well-thought designs that include user flows, information architecture, service design blueprints etc. as needed. Only then it may be possible to make a sensible comparison of tech tools and components that would best support that architecture.
Most techies have their favorite tools that they would vouch for, and some others that they disdain. They have their reasons for that, but those are not your reasons. A tool that has worked wonders for someone's project may create friction for you, while another that was a disaster for for someone else's project may just solve your most critical problem. There is no one size fits all answer to choice of tools. So please take all sorts of "Tool X rocks/sucks" advice with a grain of salt.
As I understand it, your company does not have the intrinsic capability or tech acumen to get this done with its own people. That's ok. Your core business is something else. But this is an important supporting business function, so I think it deserves some care and attention.
So my primary advice is: The first tool you need is a capable and experienced consultant. (If you were a bigger company, I'd say employ one full time, but with your current scale, a long-term contract with an independent professional or consulting firm will be more cost-effective). This consultant is supposed to guide you through the entire process of design and implementation of the systems you need. They should be your guide and advocate when you hire contractors to design or build your site/portal/whatever. They should make sure that the end result is aligned with your business goals.
The second thing you need is a solid design process that clearly defines the things you need (portal/website/etc.) for your -guess what again?- business goals. Decide with your consultant from step 1 on how to best get that. Contracting, partnering, and forming an internal team should all be on the table.
Only then you may realistically start to think about how to build these things. When you have your implementers (again, contracted, partnered or internal) and your detailed design documentation describing what you want in detail. those people should be able to make the best call on what sort of tech stack to use, in order to bring that design to life.
All this may sound daunting and arduous but it is not. The practice is established and solid. A simpler project can go through all that within weeks and go live. Even a larger project can launch in a couple of months and keep building on that afterwards.
On a side note, projects like this are living projects. they are never "done". Please account for having time/money/resources for these as long as they stay up. Going live is just the beginning.
So, start by finding your consultant :)
PS. StackShare forces me to "recommend a tool" before I can post this, so I'm "recommending" my favorite videoconferencing tool (which was recently renamed to Whereby but SS seems to have missed that). Feel free to get in touch for a video call if you have more questions :)