How to seal an OSB shed floor against pest, weather, and temperature?

Question

This question follows from my previous question about leveling my OSB shed floor. I didn't realize until I received several comments and suggestions that said question actually has two focuses:

1. How do I level my OSB shed floor?
2. How do I seal my OSB shed floor against critters, weather, and temperature?

Thus I'm copying my proposed "leveling" fix because it seems that was actually more appropriately a weatherization fix.

KNOWS AND UNKNOWNS:

• Pretty sure this OSB is not weatherized or pressure-treated already (it is golden tan, not dark green)
• I don't think the floor is inusulated, or if it is, not very well.
• I've spent time in the shed overnight sleeping in the loft. It gets cold relatively quickly in the winter, but takes until about 1 PM to get nicely warmed up.
• The doors have a tight seal for just 2x4 framing (barn style double doors)
• The windows are closed tightly and are vinyl, I believe
• The roof is metal
• There is no insulation between the rafters

In summary, I know the roof and walls are not insulated and I'm thinking If I can seal the floor and close up all the cracks that will help the situation tremendously. But, maybe I'm wrong. Imagine the whole shed is insulated, but the floor still has these gaps:

Q: Will I have problems with weather and temperature regulation because of those gaps?

Q: If I caulk the seams will I then find out those gaps were on-purpose and necessary for expansion and contraction??

When I was assisting the foreman on a vinyl siding job, he told me something that was NOT INTUITIVE. He said you have to cut the siding about 1/2" shorter than you need so that there is room for expansion. I wouldn't have known that if I was going about doing it in a DIY fashion and I'm concerned there may be some non-intuitive knowledge that I'm missing that is detrimental to me not messing things up in my attempt to fix things.

WRAP UP:

So, to recap here are my concerns:

1. I believe that cold air (in Winter) and heat and humidity could find an easy way into my shed while I'm in there through gaps in my floor seams.
2. I also want to reduce the free access cockroaches, wasps, fire ants, and other tiny pests have to get inside my shed. I believe that caulking the floor with silicone will solve my concerns about the floor and make it airtight.
3. BUT, I am concerned that I have a knowledge gap and what I don't know about what I plan to do could cause other problems and make things worse. I certainly don't want a buckled floor!

I'm really looking for guidance from those who've "been-there-done-that".