I would suggest starting with reading the IRC book all the way through multiple times.

Investing in multifamily properties offers steady cash flow, diversification, as multiple tenants reduce vacancy risks and provide consistent income.

Has anyone with experience of multiple valuations in Portugal got a view on whether banks typically under value their valuations as a norm or not? 

it looks like you have found out - correctly - that the vast, vast majority of properties for sale aren't good deals from an investment perspective. 

Contract negotiation/formulation, title company coordination, pulling comparable sales reports from their local Multiple Listing Service, rent estimation (if a rental property), neighborhood information (more important for out of state investors), and an honest/informed second opinion.

Pressure to use affiliated servicesHidden fee structuresPROFESSIONAL BOUNDARIES ⚖️Good QIs maintain:Clear fee disclosuresWritten policiesProfessional distanceEthical guidelinesWATCH OUT FOR 👀QIs who:Push investment productsOffer tax or legal advice without credentialsSuggest "creative" solutionsPromise guaranteed returns on exchange fundsBEST PRACTICES FOR VETTING 📋Check multiple referencesVerify professional membershipsResearch online presenceReview complaint historyExamine years in businessINDEPENDENCE MATTERS!

How do I access equity spread across multiple properties?

You may be able to see if a retailer still sells the 2024 version.If you can't get the one time purchase, you would need to see if the cost is beneficial.For real estate -  Quickbooks desktop > Quickbooks online because you can set up multiple entities within quickbooks desktop and not pay an additional cost per entity that Quickbooks online would charge you.Best of luck! 

I am sure there are people who did it, even on this forum I saw posts by multiple users who claimed that they were successful doing this method.

Once you pass, the shares could be a better option to move along to your family if you have multiple children in your estate.