I've seen a lot of new posters stressing over things that could have been avoided. Here is few pieces of advice I would give a newly engaged couple:
Figure out your guest list, budget and what kind of wedding you want together. They all feed off each other. THEN booked your venue.
I kind-of side-eye those who have some random number of 50 people to host and then realize their must haves = 54. OR they pick the venue then pick the guest list. Seems kind of silly not to be to pick a venue that can hold all of your 54 must haves. Instead of stressing over which 4 get the axe.
Don't get me started on the couple who picks a venue. Then find out they can't afford their guest list because they do not take inconsideration of extra fees, tips, etc or worse the bar. Why is the bar always forgotten? Look at ALL the costs before signing on that dotted line.
It's easier to find a venue when you have a pretty decent grasp of your wants and needs opposed to trying to fit into a contract you signed.
Add a buffer to your guest list. Unless you have a short 3 month engagement things change. Your truly single is now married, your BM now has a kid. Grandma might need a caretaker. Your FI forgot his co-worker was married. You are now great friends with someone you didn't even know when the list was made. Buffers allow you a little flexibility for when these things come up. If you don't need any of the buffer then you have bonus money.
STD - sometimes they do more harm then good. Bottom line is if they get a STD you have to send them an invite. If they didn't get a STD you can still invite them. Relationships change, heck finances can change. Do not lock yourself into acquaintances and non-must haves.
What kind-of advice would other old-timers give to our newly planning couples and lurkers to lower their stress?
What differentiates an average host and a great host is anticipating unexpressed needs and wants of their guests. Just because the want/need is not expressed, doesn't mean it wouldn't be appreciated.