Which plug-in could I use for midi guitar sounds, and also maybe bass?

Have you tried the included Amplitube for guitar?
There are many other guitar amp sims out there also.

For bass, maybe Helian 2nd bass(?)

I agree with Robert. Try the included Amplitube. It is my go-to amp sim. Note I purchased the latest Amplitube.

If you want to try others google/bin free amp sims and you will find quite a few. As always be aware of the risks of free software, but I did DL a couple of those free ones and they were not only malware free but they were very good.

midi, meaning you are using keyboard for guitar sounds? or, are you just wanting to plug your guitar in and use amp sims? Amplitube, Revalver, are my favs on computer, I also use ipad apps, for this.

Try these https://rekkerd.org/dsk-vsti/

Someone recomended the bass. I haven't tried any of these, but the price is right .

I use Dimension Pro but Sforzando comes with BIAB and read sfz files which is essentially what Dimension Pro does. There are many free guitar and bass sfz files about on the Web. It is really simple to load them into Sforzando and apply that to the midi track. Then to make the sound even more realistic use an amp sim (eg Amplitube which comes with BIAB) to enhance the sfz (if required). I use either TH2 or 3 on other tracks Guitar Rig as different sims produce different results. Remember that guitarists do not hit every note with the same strength so adjust the midi velocities to replicate the subtle differences in strength.

My thoughts

Tony