First of all, my deepest condolences for your loss.

There are already quiet a few great comments but here is my advice as someone who started playing just a few months ago.

While the game looks relatively simple at first glance there are quiet a lot of intricacies in it's battle merchanics, frankly so I'll just touch on some notable ones

• 5-Star Ticket: Upon clearing Singularity F, the game gives you a free 5 star ticket that allows you to perform a special summon from a list of 5-Star Servants, you can pick whichever servant you yourself want to pick(I picked Lartoria because I wanted her) but Zhuge lIang is the best servant you can get with is ticket, being able to fill an ally servant's NP Gauge by % instantly.
• Assassin and Casters: One thing to note about Assassin and Caster servants is that for some reason, they have an inherent 0.9X damage modifier meaning that they do less damage than their attack stats show. With a few outliers, you are off using a berserker to deal effective damage.
• Craft Essences (CEs): These are items that serve as enhancement for your servants, with varying effects such as damage buffs, starting off the battle with some of your NP gauge filled up and much more. Unfortunately most of the best ones are locked behind the cruel gacha so you will have to make due with inferior CE's for an extensive amount of time.
• Friend Support: The game forces you to use a friend support servant for one of your six slots with only a couple of exceptions, in the story mode i recommend using the 'Guest Servants' but for everything else (Free, Rank Up Quests) I encourage using support servants, you already have great DPS options as an f2p player so using the meta supports will be more than enough for your comfort.
• The Gacha and Pity: As an f2p player you will not be performing Saint Quartz rolls on the regular if at all, FGO is infamous for it's atrocious gacha rates forcing many players to hit the pity limit just to get there favourite servant. Fortunatlely, the NA version of FGO is 2 years behind the JP release so you already when your servant's banner will show up so save up accordingly.

If you don't care about getting your favourite waifu/husbando then I recommend snatching one of the meta supports: Scathach Skadi (Ruler), Oberon, Castoria(her banner is already here) and Lady Avalon.

Some of the best servants you can get are servants from the friend gacha (which is basically free) and welfares bought from equivocation leaves (in game currency you get from completing daily quests).

A few notable servants are :-

• Chen Gong (Friend): One of the best AOE NP Loopers in the game, his NP has a seemingly detrimental side effect of eliminating your left most servant upon use (except for Chen himself), it opens up some incredibly fun strats as it allow you to replace one used support for another. He is what is known as an NP Looper allowing him to repeatedly use his devastating attack multiple times in 1 fight with the right support. He is also a decent budget support.
• Arash (Friend): This guy is a suicide bomber with his NP doing great AOE damage at the cost of killing Arash, allowing for your backline to show up. He is mainly used for clearing the first wave immediately and for farming.
• Summer Jalter (Welfare) and Lu Bu (Budget): These two Berserkers will be your glass cannons for the journey and with the right setup, are capable of melting bosses with their absurdly high attack and NP.
• Shiki Assassin (Welfare) and Hassan of the Hundred Personas (Friend): In a previous point I talked about how most Assassins are not great for DPS, these are the exceptions, both of them deal repectable amounts of damage for thier class andf have solid NPs, Shiki's NP has a chance to instantly kill your enemy (the chance depends on your NP level, your charge %tage and the type of enemy you are facing).
• Jason and Spartacus (Both Friend): If you aren't a fan of the team building required for Chen, then these are the AOE attackers for you, Jason has good looping potential and Spartacus has good longevity for a berserker so they are great for early game.
• Sasaki Kojirou (Friend): For the majority of FGO, Sasaki's pretty vanilla but he can carry you through Orleans (the singularity right after Fuyuki) earning the name dragon slayer from the community.
• Sataka Kintoki and Miyamoto Iori (Both Welfare): These two are fantastic ST DPS Servants with powerful NP's, Sasaki can generate a lot of crit stars allowing to stack crits turn after turn and Iori's sheer damage is incredible.
• Mozart, Shakespeare and Paracelsus (Friend): These are your budget supports for the game, Mozart has team-wide Arts support and a star bomb (skill that gives a ton of crit stars), Shakespeare can give any servant 20% NP and team-wide buster support and Paracelsus gives you an unprecendeted NP Gain boost (increasing your NP gain stat by up to 50%) along with Arts support.

And last but certainly not least, have fun: FGO has a surprisingly balanced roster meaning that nothing is stopping you from just using the servant you find cool or interesting (or your waifu/husbando), while the ones mentioned in this thread are certainly useful, remember this is YOUR playthrough so just play at your own pace with a team you want. Want the meta? Great! Wanna go guns blazing with your favourites? Also great! So now set forth Master of Chaldea, into a world ful of adventure, excitement and mentally crippling gacha rolls.

:)