So I am thinking about this for a while now.
I am using a Surface Pro 3 for light office work, painting and lot's of surfing and watching/streaming videos. But it's battery life is beginning to see the end of day and I am not really using it's "desktop features" a lot.
I switched from Windows Phone to Android a year ago but I am not really that happy about some things except making my phone look like W10, which is neat. I also could live without Google...
So I am really thinking of switching to iOS for my portable casual office/artist life. I have researched a bit and it seems like Outlook and Onedrive is well integrated into iOS including contacts and calendar, which is the thing I primary use. Am I right about that? And it seems like widgets are now a thing in iOS? I want to see my calendar, news, weather, messages etc on a glance so this is one thing I really need. My last Apple products were the iPhone 3GS and iPad 2 for reference :)
While I don't wanna go all the way in terms of storage and size, I am eying the iPhone XS and the 11" iPad Pro. That would still be in my budget... but ouch anyway ;)
Yeah, if you mean letting iOS integrate your outlook contacts, it can do that. I personally don't, because my outlook contacts aren't necessarily phone numbers and i don't like that kind of mix in my contact list. Plus I use primarily iOS devices so having them synced anytime I add my appleID to a new phone is far more convenient for me. You could also add your current gmail account to sync those contacts over.
As far as calendars go, yes you can import calendars into the stock calendar and use them as your primary view. And of course if you have more than one calendar synced (like for example I have the iCloud calendar shared with my family and my Office 365 calendar for work) you can set which calendar reminders and events you add are synced with.
OneDrive app on iOS is good. I als have it set to auto backup my photos so I still have them even if I delete them from the phone/iCloud.
Widgets are available, calendar and weather, news all that standard stuff are available. Notifications are better on iOS now, especially with grouping, but there may not be as many interactions available with them as you may be used to on Android.
You cannot, however, set different default apps so you can't make the outlook app your default email program. Though in my experience there are several apps and functions that will at least give you the option of using different apps installed on your device. I encounter this a lot with websites and apps that need to open a map, for example. The 'share sheet' in iOS will open up other options for multiple things you want to do.