InvasionUS is indeed unreachable, gonna contact the devs about it
edit: they restarted it.
Servers hosted by the community aren't always reachable as it seems a lot don't have in mind to forward the port needed.... It's happening relatively often unfortunately.
I just bought this game, and I'm going to play SP for a bit longer and build up some skill before going online. Bots set at 90% Accuracy is a decent emulation correct?
90% is very low. I'd suggest you to play to start the campaign on "easy" as it should be easy enough without the enemy being totally terrible at aiming. An important tip is to drag the crosshair in the direction where you are moving or where you think enemies could come from. In this case you are "warned" soon enough and can rely on your detection advantage over the AI. Newbies also tend to not take cover too serious, but cover is one of the most important thing in this game.
But ya, you can just play some invasion online, as it's coop you don't have to be scared to get owned by veterans
How does one throw grenades on top of buildings? I generally end up blowing myself up when I try.
I modded a bit stuff in RWR (very modable game btw) so I know how grenade trajectories work (at least I think so lol). When you place your crosshair on a building top, the trajectory will be so that the apex will be in the mid of the line between you and the crosshair. So if you don't do it right (you'll get the feeling after a while), the trajectory might interfere with the collision model of the building. Also notice that you can't throw a grenade on too high roofs, 3 floors are about the maximum height.
How do I use a medkit? And what do I do with things like cigarettes and gems?
medikit is a support item, you swap between main weapon and support item/secondary by pressing "B" (see control options). When you have a medkit in your hand, then just press keep LMB pressed and it will heal a wounded comrade right in front of you and consume the medikit.
Only soldiers who are wearing vests can get wounded, eg healed.
About valuables (the different objects dropped by dead soldiers) can be picked up by pressing "F" and they go directly to the backpack. Keep in mind that when you die with valuables in your backpack those will be dropped. So if you have a really valuable item, better go put it in your stash for later use or sell it at the armory.
Also, the armory/stash doesn't seem to work for some reason. Is there some trick to it?
You need to keep "F" pressed to open the inventory. When you are in front of an armory or a stash you can interact between your inventory, the backpack and the stash/armory which are on the left side. You might think that the stash doesn't work because if it's empty it just doesn't show anything on the left side.
Does XP/Rank carry from server to server?
for invasion / campaign the profiles are persistent, just make sure when you create your nick on the server to use a password to avoid other people playing with your profile.
Classic servers don't have persistent profiles, those are getting reset after mapchange.