Sons birthday this month!

My sweet little man is turning 4 this month and I'm looking to you guys for some ideas! His birthday is the 28th and so far i have no set plans for a party, but would like to put something together. Do you recommend inviting his classmates? Or should I just keep it close friends and family? I'm also debating on where to host the party as well. I don't make a ton of money and would rather spend it on gifts than on a venue really. I'm debating between having it outside while the weather is still nice, or just having it at my house. Opinions? I think a park would be nice for all the kids but I don't want everyone to be cold or anything. What do you other November parents do? Thanks in advance guys!