Use TC as backup and NAS

Much has changed in the last few months.

1. Apple went out of the router business. They no longer make Time Capsules.

2. Back to my Mac was removed in Mojave. For most people remote connection to the TC is now far more complicated than in the past.

3. You cannot connect iOS to Time Capsule remotely at all.. and you need to use an app like filebrowser to access it even in your local network.

so for this purpose is the tc the best option?

The TC can still be useful for Time Machine local backups. And that is about the sum total. I would not buy a new TC for this purpose.. although that is up to you.

Apple is pushing you toward iCloud for remote access to your files. This is a much better approach for most people. Any files you need remotely store them in cloud.

If there are specific reasons you want to use remote access to a home network.. consider carefully using a VPN server.

Most NAS you buy (eg Synology or QNAP being the major brands) already allow excellent remote access via a number of method including vpn. Apple has taken steps to deliberately STOP you accessing files in your own network remotely. So I would move to using a NAS.. although expensive these are far superior for file storage and backup. The TC was never designed as a NAS. It is, was, and ever will be a simple target for wireless TM backups for laptops.

Some routers will include remote access to a USB drive.. the better brands like Asus or Synology do this very well. They also include VPN server and client setups.

NOTE remote access to home will not work unless you have a public IP from the ISP. Even better is a static public IP because normal domestic internet accounts use dynamic IP and that adds more complexity in needing a DDNS account. This is generally more expensive business account although some ISP will include a static IP for low usage at say $10 a month. Money better spent IMHO on your Cloud account.

You also need fast upload as well as download speeds at home, otherwise this is going to be really poor.. again cloud will always give you better speeds since you have only download to your current connection to consider. Cloud services have very high bandwidth allowances which the domestic service is not intended for.

I‘m considering to buy a Time Capsule to work as time machine and back up device

Unfortunately, Time Machine has not been all that reliable over the past few operating systems....Sierra and High Sierra. The jury is out on Mojave, so a definitive answer is not really possible. Frankly, I would not recommend Time Machine to a Time Capsule as your main backup plan.

as well to be able to remotely access the drive and access the files.

You don't indicate what operating system that you are running on your Mac(s), but Apple has removed the Back to My Mac feature from Mojave, so remote access using Apple methods is no longer possible with that operating system.....unless....your network will meet a number of other requirements that might allow port mapping. In general, you would need the following:

1) A static Public IP address from your Internet Service Provider

2) A simple modem......not a modem/router or gateway type of device

3) The Time Capsule must be set up as the "main" router for your network

No guarantees that this will work here....it is one of those things that you will have to try to see if it works.

I would like to access the drive via MBP but as well using the iPad or iPhone

Unfortunately, Apple does not want you to access the Time Capsule remotely from an iPad or iPhone or even your network, so they provide no means to do what you ask. An App like FileBrowser installed on the iPhone or iPad might be able to allow remote access to the Time Capsule, but this is an "iffy" proposition at best, involving a non-secure SMB connection, which your ISP may not allow. A quick look at the FileBrowser support area reveals that this is no longer officially supported, so add another "maybe" to this potential plan.

Bottom line......consider that the Time Capsule was introduced over 5 years ago, and Apple has not offered any hardware improvements on the product since it was introduced, so the term "long in the tooth" probably applies to the Time Capsule, which Apple officially discontinued this past April.