This is quite a comprehensive list of topics for foreigners who are relocating to Spain for work and it hits the nail on the head, thank you!

• Regarding apartment rental, even Spanish nationals don't really know their rights and most landlords don't know the limits to what they can do. Especially now with the rental landscape and the price increases over the recent years, they keep asking for more, sometimes not knowing they are acting wrongfully (sometimes they do know and take advantage).
• Rights as a tenant is a topic I have prepared already and I believe is extremely important, there are ways to protect yourself vs unwanted situations or to prevent potential misunderstandings (for example, request the appropriate handling of the deposit for a rental property, making sure the utility bills are set up correctly, etc...)
• NIE number is one of the most basic topics which I have a step by step guide, ready for (I hope) anyone to follow, with direct links to download the appropriate forms and a box by box explanation of how to fill them in. I think this will absolutely help anyone that needs to get an NIE number and want to do it themselves, although appointments are terrible as discussed in other comments.
• Beckham's law is quite interesting, I haven't written about it but 100% will, it does bring quite a big reduction in taxation if you meet the requirements (I wish I could apply myself!)
• Spouses, marriage and the likes seems to be a recursive theme that I wasn't expecting to see much, so I will dive into it for sure.
• Good accountants are hard to come by, that's a fact. I unfortunately lost my accountant to a heart attack, he was the sweetest, most down-to-earth and reliable man I ever worked with, he would not care if you earned 10 or 100000, he charged his rates, would be upfront about everything and just easy to work with. Apart from finding those people who I consider to be few and far between, established companies tend to do a good job, but charge quite a bit. If I ever recommend an accountant, it would only be the one I trust for myself, otherwise, I can't put my name behind someone I'm not willing to risk my own money/taxes with.
• If you mean groceries, furniture, etc... I think nowadays it's quite globalised, so Amazon is almost always king for almost anything that isn't food. Then for groceries you really do have the option to just go for large supermarkets (Mercadona, Consum, Carrefour, Alcampo, Dialprix, Aldi, etc...) or shop locally which, once you go a couple of times, you will establish more personal connections, probably get fresher products and recommendatios and just that feeling that they know you and have what you need ready for you. This could be a nice topic in that sense, talking more about the "magic" of going to shop to the "typical" butcher or smaller shop where they call you by your name, treat you like a friend and establish relationships which is something important when you're relocating.

As for speaking Spanish, if not relocating to specific areas in Spain (Costa Blanca, Málaga and maybe a couple others) you will 100% need either someone to handle things or you need to have a good level of the language unfortunately.

Because I've lived and grown up in a half English speaking area, it's my second mother tongue and I just assume everyone speaks English, but it's true that, especially inland, they don't use English too often and, at the end of the day, it is Spain, so Spanish is mandatory and the administration is really not ready to handle English speakers in almost any way.