20.04 vs 20.10 and backup questions
As you are still "noob", I strongly recommend you to remain, for now, on the rock solid long term release edition, Ubuntu 20.04. This way, you will be able to remain on very stable ground while you are getting more familiar with Ubuntu. Functionally, differences between the 20.04 and 20.10 release are small, and not really worth the upgrade.
Upgrading between Ubuntu releases works good in a majority releases, but not uncommonly, small issues arise, the so called "upgrade pain". It is by far better to go to a new Ubuntu version through a fresh install, although that requires putting your data back and reconfiguring your system. Staying at 20.04, which is fully supported with bug and security patches for another five years, avoids both hassles.
If you do the upgrade, you will be required to upgrade every nine months or so. Interim versions have only a short support period. Staying on 20.04 will leave you at ease for up to five years with a system that is more stable and more error free than the interim releases.
If using newer application software is your concern, do not worry. You can do that safely on 20.04 as well. The browsers, Firefox and Chromium, are always updated to the latest versions on any supported release. Snap software, i.e., software distributed in a way that is less dependent on the specific linux version, gives you, out of the box, the ability to run newer versions of software on your trusted LTS operating system. (Somewhat) more experienced users can add newer versions through third party PPA's.
In summary, there are not much reasons to upgrade from the LTS release 20.04 to 20.10, especially if you are just a "user", and especially also if you are rather new to linux.
Welcome to AskUbuntu!
Let's answer your questions one by one:
Q. Am I going to have any issues with this choice?
⇢ Nope. You shouldn't have any issues when updating to 20.10 as it's a solid release. If 20.04 is working well for you, 20.10 will be just as stable and feel a little bit faster.
Q. The 20.10 is not LTS, after the 9 months what?
⇢ You're right. 20.10 is an "interim release" where new features are introduced for people to use. There is a new release of Ubuntu every six months so, in late April, you'll see a message on your desktop asking you to upgrade to 21.04. You'll have 90 days to do so.
Q. I can not update manually the system or there will be no updates?
⇢ Not quite sure what you mean here but, if you're on 20.10 and you cannot update to 21.04 before July, you may need to make a new installation USB stick (or DVD) and install overtop your existing system. 20.10 will stop receiving security updates near the end of July 2021.
If you're looking for something that will be stable and supported for several years, feel free to stick with 20.04. A lot of people use the LTS releases because they're very well supported and have been tested thoroughly.
Hope this answers your question