Looking for some advice

Since this event gacha is a guaranteed 5* and paid only, I recommend you to get cavalry banner.

The bonus you earn from the purchase and SQ that you earned until now should be spend on something better, such as Merlin , King Hassan, or Musashi. All of those that I mentioned are on end of the year/early 2019.

Since I am a F2P too... your luck is...EX. mind to share tips?

Your lineup seems solid enough. You'll probably want to level a few of the better 3 stars to fill some holes, but you'll be fine to just spend sq on servants you like.
Arts teams generally refer to teams that field servants that use arts cards to fire off their NPs as often as possible. Buster teams usually just spam buster chains for raw damage.
As for Holy Grails, I believe we've gotten 11 so far from singularities and some events. I'd like to point out that grailing El-Melloi won't really improve his performance because the vast majority of his utility come from his skills, but feel free to do so anyway if you just like his character.

Well the question isn't so much "is your team good enough", but rather "do you like any of the servants enough to pay for them".

- Honestly, SSRs are not needed to complete any part of the game, and any team with Waver on it is almost by default "good enough". Vlad-Tamamo-Waver is considered one of the best arts teams, and Gilgamesh is one of the best (if not THE best) archers in the game.

- Yes, Ozy is unquestionably the best rider in the game and will definitely be better than Iskandar, so I recommend replacing him if you do get Ozy.

- On the topic of saving quartz, if you are buying, then no, don't save it, spend it on these banners because they guarantee you an SSR. Other than that, Merlin is the default answer for who you should be saving for.

Hey there. First let’s just call Melloi “Waver” as it’s easier. First I would say it is worth a shot with this paid gotcha. It’s only 30 PAID SQs to get an SSR (when you buy SQs the free ones don’t count towards this gotcha. Just a heads up since your F2P). I’d tou decide to I would definitely go for the Cavalry banner as it has better servants all around even though you already have some of them. The Knight banner relies on Mordred and Altera. Otherwise the servants for the most part don’t match up to the Cav banner. Ozy, Cu alter, Jack and most the others are better servants.

So you asked about Arts and other teams. From what your saying of your team comp, you’re not using your servants to the full potential. It seems like you are just going with the high damage servants. And please, I hope I don’t sound rude or anything as I don’t mean to be at all.

So with the roster you shared an example of using an Arts team would be Waver and Vlad with Tamamo as your support. You can use the Chaldea Combat uniform to switch her in if you can’t find a friend support. Basically the key is you are focusing on boosting Vlads NP since it is Arts based. Tamamo has the skill in her kit to boost Arts damage for any teammate. So if you boost Vlad with Wavers skills and Tamamo’s boost; fire off Wavers NP first to lower the enemy defense even further, then on the same turn you blast them with Vlads super boosted Arts NP. And since his Arts is boosted he will not only do greater damage but also recover his NP faster so he can even fire it again in a turn or two, especially when Tamamo uses her NP. That’s a basic idea of forming an Arts team with what you have. Your boosting the main damage dealers Arts damage and letting him/her recover NP faster.

Now if you match Atalante with Gil, you can get a bit of a Buster Crit team going. Both of them are very good at producing stars for Archer class servants that is. Especially when Atalante uses her NP. So if you can get a chain with Atalante of NP,Q,Q, extra you would generate a ton of stars. Then Gil has a kit which allows him to absorb Crit Stars at a higher rate and increase his Crit Damage. So on his turn all of his attacks would likely have a 100% chance to Crit and he would do massive damage with any sort of Buster chain. That’s a very basic idea of a Buster Crit scenario. It’s not the perfect set up but I think it gets the idea across.

I hope some of that helps. And as for Ozy replacing Iskander. They have different rolls. Iskander is good for doing dailies as he has a AOE NP were as Ozy is a ST NP and is certainly better in boss battles and raids. As I said, if you go with the gotcha, go with the Cavalry banner. Best of luck and I hope this all helps a little!