Well first, the bottom picture is a very old design of mine and isn't actually complete.! It's missing the adjustable height bed which bolts to the sides and adds a little more rigidity, but even then it's not the stiffest design in the world and uses smaller thick-walled tubes. It's also a relatively small machine and was only ever really designed for cutting woods, plastics.

Regards your design then it needs a little work, for instance, you have no supports for the bed base or any bracing between each side. Would add some supports lower down on the sides to support and brace the legs as well so it doesn't change shape when moved around.

Whether you fully weld or not is up to you but what I will tell you is that when you start going large things are not so easy to get flat or surfaces planer to each other so building in adjustment is a good idea.
To be honest, if you have never built a router before then going large can be a big mistake, esp if you are wanting to machine materials like aluminum to any degree of accuracy.

It's a very common mistake to assume it can't be any more difficult to build a large machine than a smaller one.! . . . This is the mother of all Fu@k up's because when starts to go past 4ft in length things get real funky very quickly.! Have you ever wondered why there are so few build threads showing large machines.? It's not because people haven't tried, many have tried, it's because very few succeed, and most give up well before completion.

Also, doesn't matter how thick your tubes are if the design is crap or it's poorly welded or aligned with out-of-whack surfaces, etc.

My advice is to think long and hard before you go BIG and be sure you know what you are taking on and are doing because it's super easy to get wrong.
Starting with a smaller machine would be a better idea to get the feel and knowledge for whats required to build a BIG machine, plus it can help you build the Big machine.!