Мне кажется, что процент по этому вкладу слишком низкий.

Literally, мне кажется means it seems to me.

In natural English, it can often be translated as:

• I think
• it seems to me
• it feels like

It is a very common way to give an opinion a little less directly than я думаю. So it can sound softer or less categorical.

For example:

• Мне кажется, он прав. = It seems to me that he is right / I think he is right.

Because the verb казаться works differently from English think.

With казаться, the person who has the impression goes in the dative case:

• мне кажется = it seems to me
• тебе кажется = it seems to you
• нам кажется = it seems to us

So мне is not the subject here. It is the person experiencing the impression.

Russian often uses казаться in an impersonal way.

English needs a dummy subject: it seems.
Russian usually does not say that it explicitly, so you just get:

• Мне кажется... = It seems to me...

So кажется is the normal 3rd person singular form, even though no separate subject word appears.

Yes, in this sentence что is the normal way to introduce the clause after мне кажется.

• Мне кажется, что процент по этому вкладу слишком низкий.

Here что means that.

In everyday speech, Russians sometimes drop что, especially in shorter or looser sentences, but with a full clause like this, keeping что is the standard and safest choice.

Good question. In financial Russian:

• процент often means rate / percentage
• проценты often means interest payments or percentages in the plural

So here процент по этому вкладу means something like:

• the interest rate on this deposit
• the interest on this deposit

If you want a more explicit phrase, Russian also uses:

• процентная ставка по вкладу = interest rate on the deposit

Here по takes the dative case.

That is why:

• этот вклад becomes этому вкладу

In banking and official-style language, по is very common in meanings like:

• on
• for
• under

So:

• процент по вкладу = interest on a deposit
• выплата по договору = payment under a contract

Here вклад means a bank deposit or savings deposit.

In other contexts, вклад can also mean contribution, but in this sentence it is clearly financial.

So по этому вкладу means on this deposit account / on this bank deposit.

Because низкий is describing процент.

• процент is masculine singular
• so the adjective must also be masculine singular: низкий

This is a predicate adjective structure:

• процент ... низкий = the rate is low

Russian adjectives agree with the noun they describe in gender, number, and case.

Because in Russian, the verb to be in the present tense is usually omitted.

So:

• процент по этому вкладу слишком низкий

literally looks like:

• interest on this deposit too low

but it means:

• the interest rate on this deposit is too low

This is completely normal Russian grammar.

This is an important difference:

• очень низкий = very low
• слишком низкий = too low

So слишком implies that the rate is lower than acceptable or lower than desired.

That makes the sentence more evaluative or critical.

Yes. Russian word order is flexible, and changing it changes the emphasis more than the basic meaning.

The original version is natural and neutral:

• Мне кажется, что процент по этому вкладу слишком низкий.

Other possible versions:

• Мне кажется, что по этому вкладу процент слишком низкий.
  This puts a little more focus on this deposit.

• Мне кажется, что слишком низкий процент по этому вкладу.
  This emphasizes too low more strongly.

So the original word order is a good standard version, but it is not the only possible one.

They can both be translated as I think, but they are not exactly the same.

• я думаю = I think in a more direct, deliberate sense
• мне кажется = it seems to me, often softer and a bit less absolute

Compare:

• Я думаю, что процент низкий. = I think the rate is low.
• Мне кажется, что процент низкий. = It seems to me that the rate is low.

So in your sentence, мне кажется makes the opinion sound slightly less blunt.