stringyquark

Not sure about weight, but most of my builds are in the four to five hundred part range. Mostly struts

It can be a steep learning curve. I was able to get to orbit, land on mun, rendezvous and dock, and make duna orbit before adding mech jeb. There are many excellent tutorials on YouTube that will aid you to do all of it without mods. I am not saying there's anything bad about mods, you just don't need them. Biggest issue I had with steering was docking, I would start looking at the ship I was docking with and start seeing funny because of my orientation. Switching to chase cam helped with this a lot. So imho you don't need mods, but I did start using mech jeb for some of the info it provides otherwise I am stock everything else. Biggest tip would be check those helpful YouTube vids for what you're having issues with, quick save often, and rejoice in the joy of failure. Killing kerbals learning was some of my most fun and memorable moments!

They removed end flight for me because I lost waytoo many stations accidentally hitting it trying to hit the space center button.

I like yogurt. Landed many capsules in the ocean, kerbals in space suits float nice and kerbals dog paddle well! But I believe if you took there space suits away they would sink like stones. Kerbals are dense like their planet. At least in my mind.