Hi, Impulse! It's not bad at all

The most frequent mistake you do is aspects. You tend to use imperfective where perfective is needed. I would advise you paying more attention to this thing. There are also some other small errors. And your punctuation also leaves some space to improve it.

Сегодня утром (no comma) я ездил в новый ресторан, который я нашёл на прошлой неделе.

1) We say: в этом (прошлом, следующем) году, в этом (прошлом, следующем) месяце but на этой (прошлой, следующей) неделе.
2) You do not need a comma after time modifiers like "сегодня утром" etc. It's just a sentence member which does not need to be separated wherever you put it.
3) But you need a comma between clauses. The conjunction word "который" is used to connect two separate clauses. So, a comma is mandatory before it.

Я хотел позавтракать там.

1) You need perfective: "позавтракать" since it's a single completed action. If you say "Я хотел завтракать там", it would be understood as "from now on; on the regular base".
2) "Туда" is a direction (to there, to that place). You mostly use it with words of motion. "Там" is just a location (there, at that place).

Я заказал русский завтрак: икру, оладьи на кислом молоке, омлет с водкой и лососем, морковники.

1) "Сделал заказ" can be used, but it sounds too official. Moreover, "сделал заказ" cannot have a direct object, so you cannot say "Я сделал заказ русский завтрак". It is grammatically wrong. If you want to stick to "сделал заказ", you just have to list items like that:

- Я сделал заказ: икра, оладьи, ...

"Заказал" is much better, and it is transitive (so, you can specify "заказал что").

2) We use a colon ( : ), not a dash, after a general word and before a list of specific items. Русский завтрак: икра, оладьи, ...
If you list items first, and then summarize them, then yes, use a dash: Икра, оладьи, ... - русский завтрак.

3) Since "заказал" is transitive, it requires accusative. So, I have put "икра" to accusative (икру).

Всё было очень вкусно, мне понравилось.

1) You used "всё" (everything) correctly. But it is used in singular in Russian, and it is neuter. Therefore, you say "всё было" (not "были").
Probably, you also know "все" (everybody). Then it is plural. Please compare:

- Всё было очень вкусно, мне понравилось. (Inanimate: Everything was very tasty, I liked it).
- Все были очень добрыми, мне понравились. (Animate: Everybody was very kind, I liked them).

2) You have three options of the adjectival predicate (the part after "было") in the past:

2-1: Всё было очень вкусно. (Adverbial state form) It is the best option here, since "всё" is abstract. You can even omit "всё" and say just "было очень вкусно" (it was very tasty).
2-2: Всё было очень вкусное. (Adjectival form, nominative singular neuter). Here "вкусное" is linked to "всё" (because it is singular neuter). So, "всё" cannot be omitted. This option is also correct, but it is the worst option among those three.
2-3. Всё было очень вкусным. (Adjectival form, instrumental singular neuter). It is a bit better that 2-2, because it is more natural to use instrumental in past or in future (after "было" or "будет").

3) "Понравилось" agrees with "всё" (singular neuter).
It is better to say "мне очень понравилось".
The subject of "понравилось" can be omitted, since it is the same as in the first part:
Всё было очень вкусно, и мне всё очень понравилось. - It is the full sentence. Not "он" (русский завтрак), but "всё" (since it logically follows from the first part). But not to be redundant, we would just omit its mentioning again:
Всё было очень вкусно, мне очень понравилось.

Ресторан тоже понравился мне.

1) Понравился. You use -ся after a consonant. The truncated version -сь is only used after a vowel, compare:
Понравился, понравилась, понравилось, понравились.
Понравлюсь, понравишься, понравится, понравимся, понравитесь, понравятся.

It is easy to remeber, since it is just physically difficult to pronounce truncated -сь after a consonant. "Понравилсь" would be hard to pronounce, wouldn't it?

2) Although it is correct to say "Ресторан тоже понравился мне", it would be much more natural to arrange it as "Ресторан мне тоже понравился". We tend to put a pronoun (like "мне") before a verb.

Картины на стенах были приятные, стены яркие, официантки были дружелюбные, и цены - не очень высокие.

1) "цвет стен" is too official.
Although, you can say "Картины на стенах были приятные, цвет стен синий", ... ("цвет" is singular). But it is better to rephrase it like "Картины на стенах были приятные, стены синие" - much more colloquial.
Moreover, "яркий" (bright) is not actually a color. I would not say "цвет стен яркий". It can be disputable, but I believe "цвет" is something specific (красный, белый, синий...). "Яркий" is just a property of the walls: "стены яркие" - that's enough.

2) "цены" is in plural, so you need the adjective in plural.
Then, something can be cheap or expensive (фрукты дешёвые, напитки дорогие etc.). But prices cannot be cheap or expensive, they are not a subject to buy You don't buy A PRICE of food, you buy FOOD, don't you So, prices can only be high or low.

But frankly speaking, "дорогие цены" or "дешёвые цены" is a logical mistake which some Russian speakers also do.

3) I would prefer putting all the adjectival predicates into instrumental. As I mentioned above, it is more natural for past or future:
Картины на стенах были приятными, стены яркими, официантки были дружелюбными, и цены - не очень высокими.
I like this version more

Мне нравится кухня этого ресторана.

1) It is "кухня".
2) Although "кухня этого ресторана" is grammatically good, it sounds a bit formal.
I would better say
Мне нравится кухня в этом ресторане.

Я точно вернусь/приеду ещё раз в этот ресторан.

1) Here "точно" means "definitely", "for sure", right? Then it relates to the verb, and it is logical to put it before the verb. It does not sound right in the beginning of the sentence. You can also replace it with "наверняка":

Я точно/наверняка вернусь ... - both are good.

2) "буду вернуться" is impossible. "Вернуться" is perfective, and the future of perfective verbs cannot be formed with "буду". "Буду" only works for imperfective verbs. "Вернуться" in future is "вернусь".
"Ещё раз" is a single action (one more time). So, it requires perfective. Therefore, your second option (буду ездить) does not work either. By itself, "буду ездить" is grammatically correct (imperfective future). But it does not agree with "ещё раз".

3) Этот ресторан (it is masculine, so ЭТОТ).