Welcome to CC! *waves back*
Always good to have another AFOL emerge from their dark age, and also more women in what is sometimes perceived as a boys' club (not true, btw, two of our ten site officials are from the fair sex).
Don't worry about feeling intimidated by other builders. We've got people at all skill levels, and everyone starts somewhere (see, for instance, the my first MOC
thread). Heck, I've been doing this for years and help run this place, and I'm intimidated by a lot of the builders I see. But it's all fun here and we're a fairly encouraging bunch.
On a similar note, don't be intimidated by the fact that some have much larger collections. Again, we all start somewhere, and even if you just buy a little LEGO here and there, in a few years you've got a massive collection.
On the "keeping them for the grandkids" issue, I have a question. Are these actual grandkids who love to come to grandma and grandpa's and play with their LEGO, or is it more of a "Someday we want to have grandkids - hey, btw, why don't you have kids yet?" sort of thing? If the former, I guess I can see their point and you'll have a hard time getting them. If it's more of a 'someday' thing, you can always just promise to give them back later if they need them (by that time you'll probably have amassed a larger collection anyway, see above). If there are no grandkids yet, it's at least four years before these potential grandkids would play with them anyway. It's not like you want to take the LEGO so you can sell it at a garage sale; it's always going to be right there in your home. Besides, these potential grandkids are either going to be your kids or your nieces and nephews, so it's not like having the LEGO at your house is keeping it from the grandkids. For years my folks have had lots of our old toys, books, etc at their house for just this reason, but since my kids are the youngest (mine are 4 and 2 while my youngest niece is 10), my folks have started bringing the little kids stuff to my house. Basically, they figure, my sisters' kids don't want them any more, and it's better for my kids to have access to them every day rather than the occasional visit to Grandpa and Grandma's (especially since we live a long ways away and it's much easier for my folks to come visit us than for us to go there).
Anyway, that's a long ways around the question to say that you can probably convince your dad that it's better to have the LEGO at your place being used than simply sitting on a shelf waiting for a grandkid.
BTW, you should really go on that Discovery Center tour.