Sea hexes, I believe, give 1 research, even if you don't have the upgrade. If you get Naval Mines, they give one research and one industry.
SIZE
You make units with industry. Now, units have a "size". This is how many "points" they have. Usually, each point of a stat - armor, attack, shields, etc. - is worth one point of size. Engines are a little different. Engines for naval units, sea and space, are 1 point. Engines for air units are only 0.5 points. And engines for land units are 2 points. So, a 1/1/0/1 land tank (attack/armor/shields/engines) has 1+1+2 size points and a point value of 4.
STAT TECHS
However, there's a "soft cap" on how big you can make your stats. This is determined by your stat techs - weapons, engines, etc. Suppose I have Land Weapons 4. Then, 1 weapon point on a tank will cost 1 size point, 2 will cost 2, and so on, up to 4. So, a tank with 4/1/0/1 costs 4+1+2=7 points. Now, suppose I go one step farther, and have a tank with 5 weapon points. That extra weapon point will cost 2 size points, not just one. So 5/1/0/1 costs 9 points, 6/1/0/1 costs 11, and so on. This is true up to twice my Land Weapons technology, which is 8. So 8/1/0/1 costs (4*1+4*2)+1+2=15 points. When I try to go farther, the extra points now cost three points each - so 8/1/0/1 costs 18 points - this is true up to 3 times my land weapons technology, or 12. And so on.
SIZE TECHS
Normally, each point costs 1 industry. So my 1/1/0/1 land tank is 4 points large, and 4 industry to produce. Carrying capacity points are different. They cost one point each but only half an industry. So assuming I have the proper techs, a 1/1/0/1 land tank with 4 carrying capacity would be 1+1+2+4 = 8 points, but only 1+1+2+(4*0.5) = 6 industry.
There is also a "soft cap" on size. For each point of size tech you have for a type of unit (e.g. Land Size for land units), you will have four points where everything will be normal. If I have Land Size 3, and I build a 12 point unit (no carrying capacity), it will cost 12 industry. Now suppose I try to rise above my proper station and build a 13 point unit with only Land Size 3, which allows 3*4=12 points of normality. I have broken my "soft cap". The industry cost now is (POINTS USED)^(POINTS USED/SOFT CAP). My soft cap is 12, as we have established, and I have used 13 points. So the industry cost is 13 to the power of 13/12, or about 16. A 14 point unit would cost 14^(14/12), or 22 points. As you can see, breaching your soft cap comes at a steep price. It may sometimes be worth it, though.