How much will I need RAM to run windows 10 inside Virtual Box in Ubuntu

I use Ubuntu a lot for programming and coding, but due to my studies I'm starting to need some Windows apps a lot like excel, word and other softwares sometimes (PowerBI and other)

Currently I have Ubuntu installed with windows in a dual boot setup, Ubuntu has around 194 GB of hard drive while windows has much more, in case I can get windows running well in a VM, I might remove windows totally from Dual Boot.

My Machine runs on an Intel core I5 4th generation, has a total ram of 8gb (DDR3) and Ubuntu has around 90gb of storage available.

Is this enough to let me run Windows 10 with basic office apps smoothly and some other non-heavy windows only software on the virtual box ?

It will be difficult to answer this because the question can only be answered with opinion. We can try to break the question down, though:

Is this enough to let me run Windows 10 [in] VirtualBox?

Yes. You can allocate 4GB of RAM to the VM and make sure your browsers are closed on the host before starting Windows to ensure there are enough physical resources available. Be sure to have a swap file of 12GB or more, though. If there is not enough memory available to the host, everything could lock up. More swap isn’t always the answer, but it can reduce the pain of a complete freeze.

Is this enough to let me run Windows 10 with basic office apps smoothly [in] VirtualBox?

What is “smooth” for one person may be very different from your perspective. This will result in a great deal of opinion-based answers, which are not always helpful.

Is this enough to let me run Windows 10 with basic office apps smoothly and some other non-heavy Windows only software [in] VirtualBox?

Define “non-heavy”. For me, SQL Server Management Studio would be considered “non-heavy before noon”, as it can do a lot with very little resources … until I start working with large return datasets. Same with some sites running in Edge. Reading AskUbuntu will be easy. Using Google Maps will kill the machine. Just like the previous question, the answer can only come from you.

A suggestion:

Virtual machines are “cheap”. Give it a try and see if your computer can give you the performance you need with VirtualBox. If you can upgrade the RAM, that will give you more breathing room. If you can allocate more than 4GB to the VM without locking up the host OS, that might be a good way to get a little more performance (generally the host needs at least 4GB remaining for its own processes). If you need to buy Windows and don’t want risk losing money, consider trying out a pre-built VM from Microsoft for 90 days to see if your machine can handle the workload.

At the end of the day, the only person who can answer this question correctly is you 👍🏻