Not really. I save the 30 gold for something like protection for the real units. I only use the mercs for bodies to cap opening resources.

currently i am working on a deck which uses all cards in the first three rounds. and if everything is working quite as i want it to i can get away easily afterwards by having a very huge advantage. one thing for me i oven notice in sealed tourneys i end up having cards like the marksman heavy tank till the end of the game. i take those cards in the beginning nad never use them which is awfull because i also think you should pick your cards and construct your decks in a way that this will not happen to you. it just not feels right to have cards left at the end of the game those should have been used earlier or not even get picked.

Yesterday I lost to Mythos when he used 8 cards and all the money in first turn.

Personally i use 5-6 cards at the start, but i think the beauty of the game, as another has mentioned, is that there are tons of ways to play the game to fit your style. Its like Chess, or Shogi, or Go, or Xiangqi, or Starcraft 2. A true strategic game is not simply do this every game to win. Dont do it and you lose. It is instead something that allows creativity while still having basic rules of thumb that when learned divide noobs from average from pros. This is why i love this game so much. It allows the perfect amount of creativity while not completely basing it on creativity and luck.

Jojo for instance is apparently trying to make a deck that uses all cards in the first three turns

Fewar likes to keep his cards later on than the early game. Though he has not been extremely successful against Jojo's way of playing, i think modifications and just a couple more cards used at the start would make Fewar's style very viable.

I think that for beginner's you should generally use at least 5 at the start. 4 or below feels a bit low. But if you can make a low amount used at the start work, great power to you for doing what you want to do successfully.

Wait what? Jojo is the only one I am succesful now

What i also consider very important when building a deck ( i know its pretty obvious, but still) is the size of a map. I find that many times the size of the map affects greatly how many cards i will use in the first turns. If its a small map, maybe you will want to rush your oponent, in which case i use almost all of my cards in the first turn. If its a big map, i carry some debuffs because when i spread my units i could encounter the one that can wreck mine. In the end, as many said before, there is no right or wrong, only different play styles.

I personally only using about 4-5 card at the beginning , usually those are enlist, movement and vision
As for merc, the rule of thumb is, only using merc for any task that require putting the merc on suicide mission like being a meat tank, capping resource, or surveying enemies troops
However, never use merc for something that does not suppose to be dead soon like artilery (merc arti is utterly pointless as it only cost 15 gold less and artillery not suppose to be dead soon anyway)

As for using a lot of card on the beginning, i think it's okay since you would get an upper hand but i personally like to keep some card that essentially important on mid to late game like airlift 2 or minor artillery (this one is a must have on my deck)
Having those card is handy and could pretty much help on any situation (you could even use airlift to evacuate your unit)

i dunno... that extra 15 g has been the bane of my existence and my savior for many a game now

Merc Artillery costs 65g. Regular artillery costs 125g, that is a 60g difference. Enlist Artillery is 90g, so it is still a much bigger gold difference than 15g.

Taking merc artilery might be good only if you go for base rush.

Or maybe in sealed on small map when you dont have anything better.