Hiya, I have been on this server just over a year now so I am happy to answer your questions.
1. Destiny does have a small community though during events and happy hour you can expect to start games and people will readily join them, simply put a big JOIN in your game name and they should roll right in. If they don't, you can shoot a message out on the destiny discord and folks will usually jump on to join a game. During happy hour all rare drop rates are x3 what they normally are. Happy hours last for 3 hours and occur every 15.5 hours. The current event is Halloween event and will last for about 4 more weeks, during which section id change is unlimited and exp is x10 (exp is x5 when no event is going on). Lots of other good drops in for event as well for both the new and veteran players. I think of the community like a small town, you see the same folks alot and everyone always happy to give you a hearty welcome.
2. When you are in multiplayer mode on ultimate difficulty, the drop rate is always x2 so pretty much cut in half those numbers you see on drop table as long as you plan on playing in multiplayer mode when you get to ultimate. As I mentioned above, happy hour makes it even easier to find rares since rare drops have x3 rate. That x3 rate is for all difficulties/modes, allowing players still going through those lower difficulties to grab some sweet rares too whether they are playing in solo or multiplayer mode. For example, the ep1 rate for Cent/battle from Hildetorr on ultimate Viridia will go from 1/16 to 1/8 as long as you are in multiplayer mode. During happy hour that rate will go to 1/5.3 regardless of if you are in multiplayer or single player mode. Cent/battle gives a 80% atk speed bonus, good stuff.
3. Almost all the custom items are available all year around. Usually there are a few items that come with a seasonal event like Halloween or Christmas but even those will come back when the holiday comes around again. Even then you can certainly buy seasonal items from other players. You can hunt parasitic gene flow year-round here though the drop rate is better for it during Christmas event. The vanilla weapons have also started to receive buffs to put them more in line with all the custom equipment as well. Just take a look at the drop table and you will see loads of custom gear on there. Most are on ultimate difficulty though there are a few on very hard as well now.
4. We have infinite mag feed all the time, there is no mag feed timer so you can feed your mag all at once. Look up a max stat plan for you character on the discord tab for it and feed your mag first as you will start with a big chunk of meseta too. Or just feed a mag how you want to and then make one for your max stats later, can also start new characters to deposit baby mags in shared common bank. Alternatively just get into ye ol open forest game and start watching those levels fly so get right into the action.
If you should decide to join Destiny there are certainly lots of folks to help you get started (including myself). You can join the discord from the forum home page, that has everything you need to know about the server in well organized tabs and a bustling community to reach out to.