Planting outside is more beneficial with Seasons, as rain will keep your plants watered. One less thing you need to do yourself. Besides, My garden is too big to fit indoors. I have every plant growing in it except the 10 from the National Park and the 3 from Sixam.
I don't personally have much trouble getting plants. I usually cheat for money and buy certain things, like seed packets and VoidCritters card packs, in large quantities. If any plants are missing, I usually know where they can be found or, in some cases, how to graft for them. This whole thing with the weeds option is just baffling, though. I've used the Shift+Click menu with my plants (obviously, this needs testingcheats to be on). I used it to evolve all my plants to Perfect status. I have a suspicion that "Mulching" might slow or prevent the appearance of weeds, but I haven't seen any weeds for a while anyway. It's late fall right now in my game and Patchy does a pretty good job at weed control anyway, so if that's what it does, I may not even notice any effect.