A little webshop adjunct to existing website with authorisation

I have an existing godaddy website which has constraints. I want to offer clients the opportunity to order from the website, enter information, run some processing in the background, select payment options from with invoice in the normal way, prompt payment (and possibly paypal/stripe) with a discount, discount codes. I want the option for multiple offerings which are tailored to groups of clients so some clients will only see some and discounts for clients preferably managed based on microsoft oauth or similar authentication to get in so the client needs to be in a group to see offers and some offers anyone can see if they log in, I want to track who logs in and I want to manage the access list easily (we have about 10-20k contacts we'd like to pre-register in groups). We are doing some coding in python to do calculations for forms and we could host the calculations on another service so the website is simple js calling that, but if the hosting platform can run a bit of python rather than php (just because we use that internally, although we can live with other stuff) that's a bonus, and it may need to host a db of several hundred thousand records. We were going to do this ourselves within what GoDaddy hosting allows but I thought I'd see if we can take the step now. I have other domains so can link a dedicated domain to an independently hosted site. We want to be able to edit and manage ourselves to add more offerings easily. I would like someone who knows their stuff (all of the above is I assume bog-standard trivial here's one I made earlier if you're used to this - we will help put the forms and branding together and code the logic) to give me a sensible suggestion including suggesting hosting provider options at sensible ongoing cost without strings and payment channels (stripe and paypal can connect to xero/revolut/wise, am open to suggestions, most clients will probably pay by invoice and platform fees need to be small or won't work on services where we are paying out fees) etc - we're not expecting much traffic. I'd like someone human I can have a straightforward conversation with about what makes sense appreciates that we have a reasonable idea what we're doing but aren't expert in setting up external websites but don't want be sold some website design for silly money. I'm guessing it's only a few hours actual work to set up once we have agreed what to do and you know what data we have and plan to use. We're using Mongodb internally but we can export the data we need for this as required. I'm hoping I've put off many people with this deliberately dense rambling requirements but if you've read this far and get where we are going, please get in touch. If you send an automated reply saying I have read and understood your requirements and paraphrase them you will automatically disqualify yourself! I've just started using freelancer, have a small flexible team, don't want to pay any more than I have to but happy to pay for expertise and if you can do this efficiently there'll probably be more things along the way.