Whether or not you need to size the bullets depends on the size of your chamber and the diameter of the cast bullet. Not every mold is the same, and most are designed to drop 0.002" to 0.004" over the target diameter. Some also drop oblong bullets - bullets that are not actually round.
If the bullet is large enough in diameter, or out of round far enough, that a loaded round cannot even chamber in your firearm... then they
must be sized. You can't get around it. But, don't worry about the expense. You can get a Lee push-through sizing die kit for $15-18, or just the sizing die for as little as $8. They work with any 7/8-14 (standard) reloading press.
Gas checks? Depends on how hard you want to push the bullets, and what alloy you're using.
Personally, I've never used a gas check for 9mm.
Whatever you decide to do... Be sure to shop around for the equipment. Ebay, from what I have seen, is usually a bad place for casting equipment. Most of the equipment on Ebay is worn out, damaged, being over-hyped by the seller as something "rare", or has bidders that get caught up in a bidding war. If you're on a budget, avoid Ebay.
Case in point - That mold you used as an example can be picked up on sale for the same price,
new; and you can routinely find it for $18-20, new. (I recently purchased a few new 2-cavity Lee molds for $13 / apiece.)
The Bullet Casting forum here, the Lyman Cast Bullet Handbook, Modern Reloading (Lee manual), and
http://castboolits.gunloads.com/ are decent places to get more information on the subject.