your questions are very ambiguous, I don't think many people will understand what you're asking. Can you please re-phrase them? If you don't know how to ask something please use google translate as the output will be clearer...
As far as I know, multisites have the same IP and if you intend on using multisites as your own PBN you'll be in a lot of troubles (it might even de-rank all of your sites that are linked together), so multisite and PBN should not be mentioned together....
Regarding your last question (the only one that I - somewhat - understand) I can say these:
a) web 2.0s are sites that allow you to sign up and publish content on their platform for free. Due to their nature (free) google doesn't see much value in backlinks coming from these websites, which is why web 2.0s don't have enough ranking power. In order to get enough SEO value from web 2.0s you need to treat them like your own money sites, which means: build them up with content and authority (backlinks) and wait for the link juice and the age of the content to do its magic, but if you invest so much time and so many resources into making web 2.0s work you'd be better off focusing on your own PBN and money sites instead since - at least with your PBN and money sites - you won't have to worry about 3rd parties taking your sites down like it's the case with many web 2.0s that force you to upgrade to paid membership, or they noindex / nofollow your links, or close your accounts for inactivity, or shadowban your posts, etc...
Personally, I don't recommend you focus any of your precious time, energy and resources on building up web 2.0s beyond the point of just publishing a piece of content with a link back to your site inside of it, and then moving on. But that's me!
b) the differences between PBNs and guest posting sites can be looked at from 2 perspectives: the perspective of the owner of a PBN / guest posting site, and the perspective of the user.
From the perspective of the owner I can't say too much since I've never owned PBNs. I did own guest posting sites, but not as a business (I didn't have 100s of sites that are created specifically to sell guest posts, I only had a handful of sites that - sometimes - I sold 1 or 2 guest posts on, so this is as far as my experience, as an owner, with guest posting sites goes).
But - from the perspective of users - the differences between PBNs and guest posting sites which, in all honesty, are just real websites (or money sites as they're also called) are these:
- quality PBNs usually require monthly / yearly fees since they are so good and powerful that they need ongoing fees to survive and do their magic. If PBN sellers sell you PBN links for a once-off fee this usually means that the power of that link will go down in value over time because the owner of that PBN has no intention, or no resources to keep his PBN alive and strong enough to continue providing the ranking power for everyone that uses that PBN.
One important characteristic of PBNs is that they have low OBLs, and low OBLs means less link juice lost, which means more link juice for the users of that PBN (you, for example).
- guest posts, on the other hand, are pretty useless (in terms of SEO) in the beginning (until the guest post picks enough link juice to be able to transfer a part of it on to your site), but they can be valuable traffic sources if the guest post is properly promoted and featured on the site and if the site is highly popular to begin with.
- another difference between PBNs and guest posts is that PBNs cost monthly fees (which I already mentioned earlier), but guest posts are always one-time fees. So, if you know that you can't afford paying monthly for your backlinks I recommend you find guest posts, web 2.0s, etc... basically any other type of backlink except for PBNs. If you do find a PBN seller that charges you a one-time fee for PBN links expect at any time for that link to disappear from the PBN, or to lose its value as time goes on, or to even make google de-rank your site / page
- last but not least, PBN links are (usually) placed on the homepage of the PBN, which is why they're so powerful (because the homepages usually have the highest authority / link juice, so any link coming from the homepage of a quality PBN is insanely powerful, both for SEO and for traffic), while guest posts are links within an article that might or might not get indexed, might or might not get ranked, might or might not get traffic, might or might not get backlinks strong enough to pass enough link juice into your site to warrant paying the price for that guest post in the first place...
These being said, both the PBNs and the guest posts are valuable sources of link juice and traffic if you do your research and know what to get
