I've read mixed reviews on this mods. Some say it is overly difficult. Such as The Temple of Trials has a scorpion that is almost impossible to defeat as level one character. Is this true?

Yeah the Temple of Trials is extremely difficult with this mod.

I tried installing megamod and FO2 RP but my antivirus showed both had viruses and wouldn't let them install.

I don't think Megamod is compatible with the FO2 RP. It sounds like your antivirus software is just being oversensitive. I highly doubt they have viruses. If those 2 mods both have a virus inside them, there would be Fallout fans everywhere complaining about it.

That's true. It happened when it got to the Lenny files..

Started playing Megamod about two days ago, and one thing I noticed is that weapon damage output is all over the place, and has very litte to do with actual damage ranges displayed in inventory. For example in the inventory, the Spear (for my hi-str character) does 3-14 damage. I've hit basic ants for no damage, over and over again, I've also hit them for 17 and 18 damage (non-crit), and every shade in between. Same with peasants and other unarmoured NPCs. Then I saw Sulik whack a Golden Gecko with a sledgehammer for no damage 3 times in a row, before he suddenly did a 21 (non-crit) hit.

Made a new character, this time with low STR, just to test a theory. With a basic Sickle (1-6 dmg in inventory), I consistently do 8, 9, even over 10 non-crit damage. Even on Leather Armored targets. Then I had Metzger's thug hit me for 24 (!!!) damage with a basic Colt, even with my leather armor's DT and DR - non crit.

Oh and as for crits - I've had crits for 2, 1, even NO damage, at times. The rest of the time they do about the same (random) damage as non-crits, only witrh added effects.

In short - wtf is going on?! How exactly is damage calculated? Because the numbers I'm hitting (and getting hit) with, have zero to do with displayed values in inventory, worn armour, or anything I can put my finger on.

For new players, the mod is definitely harder then the base game, but in annoying ways. The above is the most egregious one. Weapons do completely random damage that has nothing to do with displayed values.